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33 results

dm-writecache.c

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  • dm-writecache.c 60.53 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     * Copyright (C) 2018 Red Hat. All rights reserved.
     *
     * This file is released under the GPL.
     */
    
    #include <linux/device-mapper.h>
    #include <linux/module.h>
    #include <linux/init.h>
    #include <linux/vmalloc.h>
    #include <linux/kthread.h>
    #include <linux/dm-io.h>
    #include <linux/dm-kcopyd.h>
    #include <linux/dax.h>
    #include <linux/pfn_t.h>
    #include <linux/libnvdimm.h>
    
    #define DM_MSG_PREFIX "writecache"
    
    #define HIGH_WATERMARK			50
    #define LOW_WATERMARK			45
    #define MAX_WRITEBACK_JOBS		0
    #define ENDIO_LATENCY			16
    #define WRITEBACK_LATENCY		64
    #define AUTOCOMMIT_BLOCKS_SSD		65536
    #define AUTOCOMMIT_BLOCKS_PMEM		64
    #define AUTOCOMMIT_MSEC			1000
    #define MAX_AGE_DIV			16
    #define MAX_AGE_UNSPECIFIED		-1UL
    
    #define BITMAP_GRANULARITY	65536
    #if BITMAP_GRANULARITY < PAGE_SIZE
    #undef BITMAP_GRANULARITY
    #define BITMAP_GRANULARITY	PAGE_SIZE
    #endif
    
    #if IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API) && IS_ENABLED(CONFIG_DAX_DRIVER)
    #define DM_WRITECACHE_HAS_PMEM
    #endif
    
    #ifdef DM_WRITECACHE_HAS_PMEM
    #define pmem_assign(dest, src)					\
    do {								\
    	typeof(dest) uniq = (src);				\
    	memcpy_flushcache(&(dest), &uniq, sizeof(dest));	\
    } while (0)
    #else
    #define pmem_assign(dest, src)	((dest) = (src))
    #endif
    
    #if defined(__HAVE_ARCH_MEMCPY_MCSAFE) && defined(DM_WRITECACHE_HAS_PMEM)
    #define DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    #endif
    
    #define MEMORY_SUPERBLOCK_MAGIC		0x23489321
    #define MEMORY_SUPERBLOCK_VERSION	1
    
    struct wc_memory_entry {
    	__le64 original_sector;
    	__le64 seq_count;
    };
    
    struct wc_memory_superblock {
    	union {
    		struct {
    			__le32 magic;
    			__le32 version;
    			__le32 block_size;
    			__le32 pad;
    			__le64 n_blocks;
    			__le64 seq_count;
    		};
    		__le64 padding[8];
    	};
    	struct wc_memory_entry entries[0];
    };
    
    struct wc_entry {
    	struct rb_node rb_node;
    	struct list_head lru;
    	unsigned short wc_list_contiguous;
    	bool write_in_progress
    #if BITS_PER_LONG == 64
    		:1
    #endif
    	;
    	unsigned long index
    #if BITS_PER_LONG == 64
    		:47
    #endif
    	;
    	unsigned long age;
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	uint64_t original_sector;
    	uint64_t seq_count;
    #endif
    };
    
    #ifdef DM_WRITECACHE_HAS_PMEM
    #define WC_MODE_PMEM(wc)			((wc)->pmem_mode)
    #define WC_MODE_FUA(wc)				((wc)->writeback_fua)
    #else
    #define WC_MODE_PMEM(wc)			false
    #define WC_MODE_FUA(wc)				false
    #endif
    #define WC_MODE_SORT_FREELIST(wc)		(!WC_MODE_PMEM(wc))
    
    struct dm_writecache {
    	struct mutex lock;
    	struct list_head lru;
    	union {
    		struct list_head freelist;
    		struct {
    			struct rb_root freetree;
    			struct wc_entry *current_free;
    		};
    	};
    	struct rb_root tree;
    
    	size_t freelist_size;
    	size_t writeback_size;
    	size_t freelist_high_watermark;
    	size_t freelist_low_watermark;
    	unsigned long max_age;
    
    	unsigned uncommitted_blocks;
    	unsigned autocommit_blocks;
    	unsigned max_writeback_jobs;
    
    	int error;
    
    	unsigned long autocommit_jiffies;
    	struct timer_list autocommit_timer;
    	struct wait_queue_head freelist_wait;
    
    	struct timer_list max_age_timer;
    
    	atomic_t bio_in_progress[2];
    	struct wait_queue_head bio_in_progress_wait[2];
    
    	struct dm_target *ti;
    	struct dm_dev *dev;
    	struct dm_dev *ssd_dev;
    	sector_t start_sector;
    	void *memory_map;
    	uint64_t memory_map_size;
    	size_t metadata_sectors;
    	size_t n_blocks;
    	uint64_t seq_count;
    	void *block_start;
    	struct wc_entry *entries;
    	unsigned block_size;
    	unsigned char block_size_bits;
    
    	bool pmem_mode:1;
    	bool writeback_fua:1;
    
    	bool overwrote_committed:1;
    	bool memory_vmapped:1;
    
    	bool high_wm_percent_set:1;
    	bool low_wm_percent_set:1;
    	bool max_writeback_jobs_set:1;
    	bool autocommit_blocks_set:1;
    	bool autocommit_time_set:1;
    	bool writeback_fua_set:1;
    	bool flush_on_suspend:1;
    	bool cleaner:1;
    
    	unsigned writeback_all;
    	struct workqueue_struct *writeback_wq;
    	struct work_struct writeback_work;
    	struct work_struct flush_work;
    
    	struct dm_io_client *dm_io;
    
    	raw_spinlock_t endio_list_lock;
    	struct list_head endio_list;
    	struct task_struct *endio_thread;
    
    	struct task_struct *flush_thread;
    	struct bio_list flush_list;
    
    	struct dm_kcopyd_client *dm_kcopyd;
    	unsigned long *dirty_bitmap;
    	unsigned dirty_bitmap_size;
    
    	struct bio_set bio_set;
    	mempool_t copy_pool;
    };
    
    #define WB_LIST_INLINE		16
    
    struct writeback_struct {
    	struct list_head endio_entry;
    	struct dm_writecache *wc;
    	struct wc_entry **wc_list;
    	unsigned wc_list_n;
    	struct wc_entry *wc_list_inline[WB_LIST_INLINE];
    	struct bio bio;
    };
    
    struct copy_struct {
    	struct list_head endio_entry;
    	struct dm_writecache *wc;
    	struct wc_entry *e;
    	unsigned n_entries;
    	int error;
    };
    
    DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(dm_writecache_throttle,
    					    "A percentage of time allocated for data copying");
    
    static void wc_lock(struct dm_writecache *wc)
    {
    	mutex_lock(&wc->lock);
    }
    
    static void wc_unlock(struct dm_writecache *wc)
    {
    	mutex_unlock(&wc->lock);
    }
    
    #ifdef DM_WRITECACHE_HAS_PMEM
    static int persistent_memory_claim(struct dm_writecache *wc)
    {
    	int r;
    	loff_t s;
    	long p, da;
    	pfn_t pfn;
    	int id;
    	struct page **pages;
    
    	wc->memory_vmapped = false;
    
    	if (!wc->ssd_dev->dax_dev) {
    		r = -EOPNOTSUPP;
    		goto err1;
    	}
    	s = wc->memory_map_size;
    	p = s >> PAGE_SHIFT;
    	if (!p) {
    		r = -EINVAL;
    		goto err1;
    	}
    	if (p != s >> PAGE_SHIFT) {
    		r = -EOVERFLOW;
    		goto err1;
    	}
    
    	id = dax_read_lock();
    
    	da = dax_direct_access(wc->ssd_dev->dax_dev, 0, p, &wc->memory_map, &pfn);
    	if (da < 0) {
    		wc->memory_map = NULL;
    		r = da;
    		goto err2;
    	}
    	if (!pfn_t_has_page(pfn)) {
    		wc->memory_map = NULL;
    		r = -EOPNOTSUPP;
    		goto err2;
    	}
    	if (da != p) {
    		long i;
    		wc->memory_map = NULL;
    		pages = kvmalloc_array(p, sizeof(struct page *), GFP_KERNEL);
    		if (!pages) {
    			r = -ENOMEM;
    			goto err2;
    		}
    		i = 0;
    		do {
    			long daa;
    			daa = dax_direct_access(wc->ssd_dev->dax_dev, i, p - i,
    						NULL, &pfn);
    			if (daa <= 0) {
    				r = daa ? daa : -EINVAL;
    				goto err3;
    			}
    			if (!pfn_t_has_page(pfn)) {
    				r = -EOPNOTSUPP;
    				goto err3;
    			}
    			while (daa-- && i < p) {
    				pages[i++] = pfn_t_to_page(pfn);
    				pfn.val++;
    			}
    		} while (i < p);
    		wc->memory_map = vmap(pages, p, VM_MAP, PAGE_KERNEL);
    		if (!wc->memory_map) {
    			r = -ENOMEM;
    			goto err3;
    		}
    		kvfree(pages);
    		wc->memory_vmapped = true;
    	}
    
    	dax_read_unlock(id);
    
    	wc->memory_map += (size_t)wc->start_sector << SECTOR_SHIFT;
    	wc->memory_map_size -= (size_t)wc->start_sector << SECTOR_SHIFT;
    
    	return 0;
    err3:
    	kvfree(pages);
    err2:
    	dax_read_unlock(id);
    err1:
    	return r;
    }
    #else
    static int persistent_memory_claim(struct dm_writecache *wc)
    {
    	BUG();
    }
    #endif
    
    static void persistent_memory_release(struct dm_writecache *wc)
    {
    	if (wc->memory_vmapped)
    		vunmap(wc->memory_map - ((size_t)wc->start_sector << SECTOR_SHIFT));
    }
    
    static struct page *persistent_memory_page(void *addr)
    {
    	if (is_vmalloc_addr(addr))
    		return vmalloc_to_page(addr);
    	else
    		return virt_to_page(addr);
    }
    
    static unsigned persistent_memory_page_offset(void *addr)
    {
    	return (unsigned long)addr & (PAGE_SIZE - 1);
    }
    
    static void persistent_memory_flush_cache(void *ptr, size_t size)
    {
    	if (is_vmalloc_addr(ptr))
    		flush_kernel_vmap_range(ptr, size);
    }
    
    static void persistent_memory_invalidate_cache(void *ptr, size_t size)
    {
    	if (is_vmalloc_addr(ptr))
    		invalidate_kernel_vmap_range(ptr, size);
    }
    
    static struct wc_memory_superblock *sb(struct dm_writecache *wc)
    {
    	return wc->memory_map;
    }
    
    static struct wc_memory_entry *memory_entry(struct dm_writecache *wc, struct wc_entry *e)
    {
    	return &sb(wc)->entries[e->index];
    }
    
    static void *memory_data(struct dm_writecache *wc, struct wc_entry *e)
    {
    	return (char *)wc->block_start + (e->index << wc->block_size_bits);
    }
    
    static sector_t cache_sector(struct dm_writecache *wc, struct wc_entry *e)
    {
    	return wc->start_sector + wc->metadata_sectors +
    		((sector_t)e->index << (wc->block_size_bits - SECTOR_SHIFT));
    }
    
    static uint64_t read_original_sector(struct dm_writecache *wc, struct wc_entry *e)
    {
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	return e->original_sector;
    #else
    	return le64_to_cpu(memory_entry(wc, e)->original_sector);
    #endif
    }
    
    static uint64_t read_seq_count(struct dm_writecache *wc, struct wc_entry *e)
    {
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	return e->seq_count;
    #else
    	return le64_to_cpu(memory_entry(wc, e)->seq_count);
    #endif
    }
    
    static void clear_seq_count(struct dm_writecache *wc, struct wc_entry *e)
    {
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	e->seq_count = -1;
    #endif
    	pmem_assign(memory_entry(wc, e)->seq_count, cpu_to_le64(-1));
    }
    
    static void write_original_sector_seq_count(struct dm_writecache *wc, struct wc_entry *e,
    					    uint64_t original_sector, uint64_t seq_count)
    {
    	struct wc_memory_entry me;
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	e->original_sector = original_sector;
    	e->seq_count = seq_count;
    #endif
    	me.original_sector = cpu_to_le64(original_sector);
    	me.seq_count = cpu_to_le64(seq_count);
    	pmem_assign(*memory_entry(wc, e), me);
    }
    
    #define writecache_error(wc, err, msg, arg...)				\
    do {									\
    	if (!cmpxchg(&(wc)->error, 0, err))				\
    		DMERR(msg, ##arg);					\
    	wake_up(&(wc)->freelist_wait);					\
    } while (0)
    
    #define writecache_has_error(wc)	(unlikely(READ_ONCE((wc)->error)))
    
    static void writecache_flush_all_metadata(struct dm_writecache *wc)
    {
    	if (!WC_MODE_PMEM(wc))
    		memset(wc->dirty_bitmap, -1, wc->dirty_bitmap_size);
    }
    
    static void writecache_flush_region(struct dm_writecache *wc, void *ptr, size_t size)
    {
    	if (!WC_MODE_PMEM(wc))
    		__set_bit(((char *)ptr - (char *)wc->memory_map) / BITMAP_GRANULARITY,
    			  wc->dirty_bitmap);
    }
    
    static void writecache_disk_flush(struct dm_writecache *wc, struct dm_dev *dev);
    
    struct io_notify {
    	struct dm_writecache *wc;
    	struct completion c;
    	atomic_t count;
    };
    
    static void writecache_notify_io(unsigned long error, void *context)
    {
    	struct io_notify *endio = context;
    
    	if (unlikely(error != 0))
    		writecache_error(endio->wc, -EIO, "error writing metadata");
    	BUG_ON(atomic_read(&endio->count) <= 0);
    	if (atomic_dec_and_test(&endio->count))
    		complete(&endio->c);
    }
    
    static void writecache_wait_for_ios(struct dm_writecache *wc, int direction)
    {
    	wait_event(wc->bio_in_progress_wait[direction],
    		   !atomic_read(&wc->bio_in_progress[direction]));
    }
    
    static void ssd_commit_flushed(struct dm_writecache *wc, bool wait_for_ios)
    {
    	struct dm_io_region region;
    	struct dm_io_request req;
    	struct io_notify endio = {
    		wc,
    		COMPLETION_INITIALIZER_ONSTACK(endio.c),
    		ATOMIC_INIT(1),
    	};
    	unsigned bitmap_bits = wc->dirty_bitmap_size * 8;
    	unsigned i = 0;
    
    	while (1) {
    		unsigned j;
    		i = find_next_bit(wc->dirty_bitmap, bitmap_bits, i);
    		if (unlikely(i == bitmap_bits))
    			break;
    		j = find_next_zero_bit(wc->dirty_bitmap, bitmap_bits, i);
    
    		region.bdev = wc->ssd_dev->bdev;
    		region.sector = (sector_t)i * (BITMAP_GRANULARITY >> SECTOR_SHIFT);
    		region.count = (sector_t)(j - i) * (BITMAP_GRANULARITY >> SECTOR_SHIFT);
    
    		if (unlikely(region.sector >= wc->metadata_sectors))
    			break;
    		if (unlikely(region.sector + region.count > wc->metadata_sectors))
    			region.count = wc->metadata_sectors - region.sector;
    
    		region.sector += wc->start_sector;
    		atomic_inc(&endio.count);
    		req.bi_op = REQ_OP_WRITE;
    		req.bi_op_flags = REQ_SYNC;
    		req.mem.type = DM_IO_VMA;
    		req.mem.ptr.vma = (char *)wc->memory_map + (size_t)i * BITMAP_GRANULARITY;
    		req.client = wc->dm_io;
    		req.notify.fn = writecache_notify_io;
    		req.notify.context = &endio;
    
    		/* writing via async dm-io (implied by notify.fn above) won't return an error */
    	        (void) dm_io(&req, 1, &region, NULL);
    		i = j;
    	}
    
    	writecache_notify_io(0, &endio);
    	wait_for_completion_io(&endio.c);
    
    	if (wait_for_ios)
    		writecache_wait_for_ios(wc, WRITE);
    
    	writecache_disk_flush(wc, wc->ssd_dev);
    
    	memset(wc->dirty_bitmap, 0, wc->dirty_bitmap_size);
    }
    
    static void writecache_commit_flushed(struct dm_writecache *wc, bool wait_for_ios)
    {
    	if (WC_MODE_PMEM(wc))
    		wmb();
    	else
    		ssd_commit_flushed(wc, wait_for_ios);
    }
    
    static void writecache_disk_flush(struct dm_writecache *wc, struct dm_dev *dev)
    {
    	int r;
    	struct dm_io_region region;
    	struct dm_io_request req;
    
    	region.bdev = dev->bdev;
    	region.sector = 0;
    	region.count = 0;
    	req.bi_op = REQ_OP_WRITE;
    	req.bi_op_flags = REQ_PREFLUSH;
    	req.mem.type = DM_IO_KMEM;
    	req.mem.ptr.addr = NULL;
    	req.client = wc->dm_io;
    	req.notify.fn = NULL;
    
    	r = dm_io(&req, 1, &region, NULL);
    	if (unlikely(r))
    		writecache_error(wc, r, "error flushing metadata: %d", r);
    }
    
    #define WFE_RETURN_FOLLOWING	1
    #define WFE_LOWEST_SEQ		2
    
    static struct wc_entry *writecache_find_entry(struct dm_writecache *wc,
    					      uint64_t block, int flags)
    {
    	struct wc_entry *e;
    	struct rb_node *node = wc->tree.rb_node;
    
    	if (unlikely(!node))
    		return NULL;
    
    	while (1) {
    		e = container_of(node, struct wc_entry, rb_node);
    		if (read_original_sector(wc, e) == block)
    			break;
    
    		node = (read_original_sector(wc, e) >= block ?
    			e->rb_node.rb_left : e->rb_node.rb_right);
    		if (unlikely(!node)) {
    			if (!(flags & WFE_RETURN_FOLLOWING))
    				return NULL;
    			if (read_original_sector(wc, e) >= block) {
    				return e;
    			} else {
    				node = rb_next(&e->rb_node);
    				if (unlikely(!node))
    					return NULL;
    				e = container_of(node, struct wc_entry, rb_node);
    				return e;
    			}
    		}
    	}
    
    	while (1) {
    		struct wc_entry *e2;
    		if (flags & WFE_LOWEST_SEQ)
    			node = rb_prev(&e->rb_node);
    		else
    			node = rb_next(&e->rb_node);
    		if (unlikely(!node))
    			return e;
    		e2 = container_of(node, struct wc_entry, rb_node);
    		if (read_original_sector(wc, e2) != block)
    			return e;
    		e = e2;
    	}
    }
    
    static void writecache_insert_entry(struct dm_writecache *wc, struct wc_entry *ins)
    {
    	struct wc_entry *e;
    	struct rb_node **node = &wc->tree.rb_node, *parent = NULL;
    
    	while (*node) {
    		e = container_of(*node, struct wc_entry, rb_node);
    		parent = &e->rb_node;
    		if (read_original_sector(wc, e) > read_original_sector(wc, ins))
    			node = &parent->rb_left;
    		else
    			node = &parent->rb_right;
    	}
    	rb_link_node(&ins->rb_node, parent, node);
    	rb_insert_color(&ins->rb_node, &wc->tree);
    	list_add(&ins->lru, &wc->lru);
    	ins->age = jiffies;
    }
    
    static void writecache_unlink(struct dm_writecache *wc, struct wc_entry *e)
    {
    	list_del(&e->lru);
    	rb_erase(&e->rb_node, &wc->tree);
    }
    
    static void writecache_add_to_freelist(struct dm_writecache *wc, struct wc_entry *e)
    {
    	if (WC_MODE_SORT_FREELIST(wc)) {
    		struct rb_node **node = &wc->freetree.rb_node, *parent = NULL;
    		if (unlikely(!*node))
    			wc->current_free = e;
    		while (*node) {
    			parent = *node;
    			if (&e->rb_node < *node)
    				node = &parent->rb_left;
    			else
    				node = &parent->rb_right;
    		}
    		rb_link_node(&e->rb_node, parent, node);
    		rb_insert_color(&e->rb_node, &wc->freetree);
    	} else {
    		list_add_tail(&e->lru, &wc->freelist);
    	}
    	wc->freelist_size++;
    }
    
    static inline void writecache_verify_watermark(struct dm_writecache *wc)
    {
    	if (unlikely(wc->freelist_size + wc->writeback_size <= wc->freelist_high_watermark))
    		queue_work(wc->writeback_wq, &wc->writeback_work);
    }
    
    static void writecache_max_age_timer(struct timer_list *t)
    {
    	struct dm_writecache *wc = from_timer(wc, t, max_age_timer);
    
    	if (!dm_suspended(wc->ti) && !writecache_has_error(wc)) {
    		queue_work(wc->writeback_wq, &wc->writeback_work);
    		mod_timer(&wc->max_age_timer, jiffies + wc->max_age / MAX_AGE_DIV);
    	}
    }
    
    static struct wc_entry *writecache_pop_from_freelist(struct dm_writecache *wc, sector_t expected_sector)
    {
    	struct wc_entry *e;
    
    	if (WC_MODE_SORT_FREELIST(wc)) {
    		struct rb_node *next;
    		if (unlikely(!wc->current_free))
    			return NULL;
    		e = wc->current_free;
    		if (expected_sector != (sector_t)-1 && unlikely(cache_sector(wc, e) != expected_sector))
    			return NULL;
    		next = rb_next(&e->rb_node);
    		rb_erase(&e->rb_node, &wc->freetree);
    		if (unlikely(!next))
    			next = rb_first(&wc->freetree);
    		wc->current_free = next ? container_of(next, struct wc_entry, rb_node) : NULL;
    	} else {
    		if (unlikely(list_empty(&wc->freelist)))
    			return NULL;
    		e = container_of(wc->freelist.next, struct wc_entry, lru);
    		if (expected_sector != (sector_t)-1 && unlikely(cache_sector(wc, e) != expected_sector))
    			return NULL;
    		list_del(&e->lru);
    	}
    	wc->freelist_size--;
    
    	writecache_verify_watermark(wc);
    
    	return e;
    }
    
    static void writecache_free_entry(struct dm_writecache *wc, struct wc_entry *e)
    {
    	writecache_unlink(wc, e);
    	writecache_add_to_freelist(wc, e);
    	clear_seq_count(wc, e);
    	writecache_flush_region(wc, memory_entry(wc, e), sizeof(struct wc_memory_entry));
    	if (unlikely(waitqueue_active(&wc->freelist_wait)))
    		wake_up(&wc->freelist_wait);
    }
    
    static void writecache_wait_on_freelist(struct dm_writecache *wc)
    {
    	DEFINE_WAIT(wait);
    
    	prepare_to_wait(&wc->freelist_wait, &wait, TASK_UNINTERRUPTIBLE);
    	wc_unlock(wc);
    	io_schedule();
    	finish_wait(&wc->freelist_wait, &wait);
    	wc_lock(wc);
    }
    
    static void writecache_poison_lists(struct dm_writecache *wc)
    {
    	/*
    	 * Catch incorrect access to these values while the device is suspended.
    	 */
    	memset(&wc->tree, -1, sizeof wc->tree);
    	wc->lru.next = LIST_POISON1;
    	wc->lru.prev = LIST_POISON2;
    	wc->freelist.next = LIST_POISON1;
    	wc->freelist.prev = LIST_POISON2;
    }
    
    static void writecache_flush_entry(struct dm_writecache *wc, struct wc_entry *e)
    {
    	writecache_flush_region(wc, memory_entry(wc, e), sizeof(struct wc_memory_entry));
    	if (WC_MODE_PMEM(wc))
    		writecache_flush_region(wc, memory_data(wc, e), wc->block_size);
    }
    
    static bool writecache_entry_is_committed(struct dm_writecache *wc, struct wc_entry *e)
    {
    	return read_seq_count(wc, e) < wc->seq_count;
    }
    
    static void writecache_flush(struct dm_writecache *wc)
    {
    	struct wc_entry *e, *e2;
    	bool need_flush_after_free;
    
    	wc->uncommitted_blocks = 0;
    	del_timer(&wc->autocommit_timer);
    
    	if (list_empty(&wc->lru))
    		return;
    
    	e = container_of(wc->lru.next, struct wc_entry, lru);
    	if (writecache_entry_is_committed(wc, e)) {
    		if (wc->overwrote_committed) {
    			writecache_wait_for_ios(wc, WRITE);
    			writecache_disk_flush(wc, wc->ssd_dev);
    			wc->overwrote_committed = false;
    		}
    		return;
    	}
    	while (1) {
    		writecache_flush_entry(wc, e);
    		if (unlikely(e->lru.next == &wc->lru))
    			break;
    		e2 = container_of(e->lru.next, struct wc_entry, lru);
    		if (writecache_entry_is_committed(wc, e2))
    			break;
    		e = e2;
    		cond_resched();
    	}
    	writecache_commit_flushed(wc, true);
    
    	wc->seq_count++;
    	pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count));
    	writecache_flush_region(wc, &sb(wc)->seq_count, sizeof sb(wc)->seq_count);
    	writecache_commit_flushed(wc, false);
    
    	wc->overwrote_committed = false;
    
    	need_flush_after_free = false;
    	while (1) {
    		/* Free another committed entry with lower seq-count */
    		struct rb_node *rb_node = rb_prev(&e->rb_node);
    
    		if (rb_node) {
    			e2 = container_of(rb_node, struct wc_entry, rb_node);
    			if (read_original_sector(wc, e2) == read_original_sector(wc, e) &&
    			    likely(!e2->write_in_progress)) {
    				writecache_free_entry(wc, e2);
    				need_flush_after_free = true;
    			}
    		}
    		if (unlikely(e->lru.prev == &wc->lru))
    			break;
    		e = container_of(e->lru.prev, struct wc_entry, lru);
    		cond_resched();
    	}
    
    	if (need_flush_after_free)
    		writecache_commit_flushed(wc, false);
    }
    
    static void writecache_flush_work(struct work_struct *work)
    {
    	struct dm_writecache *wc = container_of(work, struct dm_writecache, flush_work);
    
    	wc_lock(wc);
    	writecache_flush(wc);
    	wc_unlock(wc);
    }
    
    static void writecache_autocommit_timer(struct timer_list *t)
    {
    	struct dm_writecache *wc = from_timer(wc, t, autocommit_timer);
    	if (!writecache_has_error(wc))
    		queue_work(wc->writeback_wq, &wc->flush_work);
    }
    
    static void writecache_schedule_autocommit(struct dm_writecache *wc)
    {
    	if (!timer_pending(&wc->autocommit_timer))
    		mod_timer(&wc->autocommit_timer, jiffies + wc->autocommit_jiffies);
    }
    
    static void writecache_discard(struct dm_writecache *wc, sector_t start, sector_t end)
    {
    	struct wc_entry *e;
    	bool discarded_something = false;
    
    	e = writecache_find_entry(wc, start, WFE_RETURN_FOLLOWING | WFE_LOWEST_SEQ);
    	if (unlikely(!e))
    		return;
    
    	while (read_original_sector(wc, e) < end) {
    		struct rb_node *node = rb_next(&e->rb_node);
    
    		if (likely(!e->write_in_progress)) {
    			if (!discarded_something) {
    				writecache_wait_for_ios(wc, READ);
    				writecache_wait_for_ios(wc, WRITE);
    				discarded_something = true;
    			}
    			writecache_free_entry(wc, e);
    		}
    
    		if (unlikely(!node))
    			break;
    
    		e = container_of(node, struct wc_entry, rb_node);
    	}
    
    	if (discarded_something)
    		writecache_commit_flushed(wc, false);
    }
    
    static bool writecache_wait_for_writeback(struct dm_writecache *wc)
    {
    	if (wc->writeback_size) {
    		writecache_wait_on_freelist(wc);
    		return true;
    	}
    	return false;
    }
    
    static void writecache_suspend(struct dm_target *ti)
    {
    	struct dm_writecache *wc = ti->private;
    	bool flush_on_suspend;
    
    	del_timer_sync(&wc->autocommit_timer);
    	del_timer_sync(&wc->max_age_timer);
    
    	wc_lock(wc);
    	writecache_flush(wc);
    	flush_on_suspend = wc->flush_on_suspend;
    	if (flush_on_suspend) {
    		wc->flush_on_suspend = false;
    		wc->writeback_all++;
    		queue_work(wc->writeback_wq, &wc->writeback_work);
    	}
    	wc_unlock(wc);
    
    	drain_workqueue(wc->writeback_wq);
    
    	wc_lock(wc);
    	if (flush_on_suspend)
    		wc->writeback_all--;
    	while (writecache_wait_for_writeback(wc));
    
    	if (WC_MODE_PMEM(wc))
    		persistent_memory_flush_cache(wc->memory_map, wc->memory_map_size);
    
    	writecache_poison_lists(wc);
    
    	wc_unlock(wc);
    }
    
    static int writecache_alloc_entries(struct dm_writecache *wc)
    {
    	size_t b;
    
    	if (wc->entries)
    		return 0;
    	wc->entries = vmalloc(array_size(sizeof(struct wc_entry), wc->n_blocks));
    	if (!wc->entries)
    		return -ENOMEM;
    	for (b = 0; b < wc->n_blocks; b++) {
    		struct wc_entry *e = &wc->entries[b];
    		e->index = b;
    		e->write_in_progress = false;
    	}
    
    	return 0;
    }
    
    static void writecache_resume(struct dm_target *ti)
    {
    	struct dm_writecache *wc = ti->private;
    	size_t b;
    	bool need_flush = false;
    	__le64 sb_seq_count;
    	int r;
    
    	wc_lock(wc);
    
    	if (WC_MODE_PMEM(wc))
    		persistent_memory_invalidate_cache(wc->memory_map, wc->memory_map_size);
    
    	wc->tree = RB_ROOT;
    	INIT_LIST_HEAD(&wc->lru);
    	if (WC_MODE_SORT_FREELIST(wc)) {
    		wc->freetree = RB_ROOT;
    		wc->current_free = NULL;
    	} else {
    		INIT_LIST_HEAD(&wc->freelist);
    	}
    	wc->freelist_size = 0;
    
    	r = memcpy_mcsafe(&sb_seq_count, &sb(wc)->seq_count, sizeof(uint64_t));
    	if (r) {
    		writecache_error(wc, r, "hardware memory error when reading superblock: %d", r);
    		sb_seq_count = cpu_to_le64(0);
    	}
    	wc->seq_count = le64_to_cpu(sb_seq_count);
    
    #ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
    	for (b = 0; b < wc->n_blocks; b++) {
    		struct wc_entry *e = &wc->entries[b];
    		struct wc_memory_entry wme;
    		if (writecache_has_error(wc)) {
    			e->original_sector = -1;
    			e->seq_count = -1;
    			continue;
    		}
    		r = memcpy_mcsafe(&wme, memory_entry(wc, e), sizeof(struct wc_memory_entry));
    		if (r) {
    			writecache_error(wc, r, "hardware memory error when reading metadata entry %lu: %d",
    					 (unsigned long)b, r);
    			e->original_sector = -1;
    			e->seq_count = -1;
    		} else {
    			e->original_sector = le64_to_cpu(wme.original_sector);
    			e->seq_count = le64_to_cpu(wme.seq_count);
    		}
    	}
    #endif
    	for (b = 0; b < wc->n_blocks; b++) {
    		struct wc_entry *e = &wc->entries[b];
    		if (!writecache_entry_is_committed(wc, e)) {
    			if (read_seq_count(wc, e) != -1) {
    erase_this:
    				clear_seq_count(wc, e);
    				need_flush = true;
    			}
    			writecache_add_to_freelist(wc, e);
    		} else {
    			struct wc_entry *old;
    
    			old = writecache_find_entry(wc, read_original_sector(wc, e), 0);
    			if (!old) {
    				writecache_insert_entry(wc, e);
    			} else {
    				if (read_seq_count(wc, old) == read_seq_count(wc, e)) {
    					writecache_error(wc, -EINVAL,
    						 "two identical entries, position %llu, sector %llu, sequence %llu",
    						 (unsigned long long)b, (unsigned long long)read_original_sector(wc, e),
    						 (unsigned long long)read_seq_count(wc, e));
    				}
    				if (read_seq_count(wc, old) > read_seq_count(wc, e)) {
    					goto erase_this;
    				} else {
    					writecache_free_entry(wc, old);
    					writecache_insert_entry(wc, e);
    					need_flush = true;
    				}
    			}
    		}
    		cond_resched();
    	}
    
    	if (need_flush) {
    		writecache_flush_all_metadata(wc);
    		writecache_commit_flushed(wc, false);
    	}
    
    	writecache_verify_watermark(wc);
    
    	if (wc->max_age != MAX_AGE_UNSPECIFIED)
    		mod_timer(&wc->max_age_timer, jiffies + wc->max_age / MAX_AGE_DIV);
    
    	wc_unlock(wc);
    }
    
    static int process_flush_mesg(unsigned argc, char **argv, struct dm_writecache *wc)
    {
    	if (argc != 1)
    		return -EINVAL;
    
    	wc_lock(wc);
    	if (dm_suspended(wc->ti)) {
    		wc_unlock(wc);
    		return -EBUSY;
    	}
    	if (writecache_has_error(wc)) {
    		wc_unlock(wc);
    		return -EIO;
    	}
    
    	writecache_flush(wc);
    	wc->writeback_all++;
    	queue_work(wc->writeback_wq, &wc->writeback_work);
    	wc_unlock(wc);
    
    	flush_workqueue(wc->writeback_wq);
    
    	wc_lock(wc);
    	wc->writeback_all--;
    	if (writecache_has_error(wc)) {
    		wc_unlock(wc);
    		return -EIO;
    	}
    	wc_unlock(wc);
    
    	return 0;
    }
    
    static int process_flush_on_suspend_mesg(unsigned argc, char **argv, struct dm_writecache *wc)
    {
    	if (argc != 1)
    		return -EINVAL;
    
    	wc_lock(wc);
    	wc->flush_on_suspend = true;
    	wc_unlock(wc);
    
    	return 0;
    }
    
    static void activate_cleaner(struct dm_writecache *wc)
    {
    	wc->flush_on_suspend = true;
    	wc->cleaner = true;
    	wc->freelist_high_watermark = wc->n_blocks;
    	wc->freelist_low_watermark = wc->n_blocks;
    }
    
    static int process_cleaner_mesg(unsigned argc, char **argv, struct dm_writecache *wc)
    {
    	if (argc != 1)
    		return -EINVAL;
    
    	wc_lock(wc);
    	activate_cleaner(wc);
    	if (!dm_suspended(wc->ti))
    		writecache_verify_watermark(wc);
    	wc_unlock(wc);
    
    	return 0;
    }
    
    static int writecache_message(struct dm_target *ti, unsigned argc, char **argv,
    			      char *result, unsigned maxlen)
    {
    	int r = -EINVAL;
    	struct dm_writecache *wc = ti->private;
    
    	if (!strcasecmp(argv[0], "flush"))
    		r = process_flush_mesg(argc, argv, wc);
    	else if (!strcasecmp(argv[0], "flush_on_suspend"))
    		r = process_flush_on_suspend_mesg(argc, argv, wc);
    	else if (!strcasecmp(argv[0], "cleaner"))
    		r = process_cleaner_mesg(argc, argv, wc);
    	else
    		DMERR("unrecognised message received: %s", argv[0]);
    
    	return r;
    }
    
    static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data)
    {
    	void *buf;
    	unsigned long flags;
    	unsigned size;
    	int rw = bio_data_dir(bio);
    	unsigned remaining_size = wc->block_size;
    
    	do {
    		struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter);
    		buf = bvec_kmap_irq(&bv, &flags);
    		size = bv.bv_len;
    		if (unlikely(size > remaining_size))
    			size = remaining_size;
    
    		if (rw == READ) {
    			int r;
    			r = memcpy_mcsafe(buf, data, size);
    			flush_dcache_page(bio_page(bio));
    			if (unlikely(r)) {
    				writecache_error(wc, r, "hardware memory error when reading data: %d", r);
    				bio->bi_status = BLK_STS_IOERR;
    			}
    		} else {
    			flush_dcache_page(bio_page(bio));
    			memcpy_flushcache(data, buf, size);
    		}
    
    		bvec_kunmap_irq(buf, &flags);
    
    		data = (char *)data + size;
    		remaining_size -= size;
    		bio_advance(bio, size);
    	} while (unlikely(remaining_size));
    }
    
    static int writecache_flush_thread(void *data)
    {
    	struct dm_writecache *wc = data;
    
    	while (1) {
    		struct bio *bio;
    
    		wc_lock(wc);
    		bio = bio_list_pop(&wc->flush_list);
    		if (!bio) {
    			set_current_state(TASK_INTERRUPTIBLE);
    			wc_unlock(wc);
    
    			if (unlikely(kthread_should_stop())) {
    				set_current_state(TASK_RUNNING);
    				break;
    			}
    
    			schedule();
    			continue;
    		}
    
    		if (bio_op(bio) == REQ_OP_DISCARD) {
    			writecache_discard(wc, bio->bi_iter.bi_sector,
    					   bio_end_sector(bio));
    			wc_unlock(wc);
    			bio_set_dev(bio, wc->dev->bdev);
    			generic_make_request(bio);
    		} else {
    			writecache_flush(wc);
    			wc_unlock(wc);
    			if (writecache_has_error(wc))
    				bio->bi_status = BLK_STS_IOERR;
    			bio_endio(bio);
    		}
    	}
    
    	return 0;
    }
    
    static void writecache_offload_bio(struct dm_writecache *wc, struct bio *bio)
    {
    	if (bio_list_empty(&wc->flush_list))
    		wake_up_process(wc->flush_thread);
    	bio_list_add(&wc->flush_list, bio);
    }
    
    static int writecache_map(struct dm_target *ti, struct bio *bio)
    {
    	struct wc_entry *e;
    	struct dm_writecache *wc = ti->private;
    
    	bio->bi_private = NULL;
    
    	wc_lock(wc);
    
    	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
    		if (writecache_has_error(wc))
    			goto unlock_error;
    		if (WC_MODE_PMEM(wc)) {
    			writecache_flush(wc);
    			if (writecache_has_error(wc))
    				goto unlock_error;
    			goto unlock_submit;
    		} else {
    			writecache_offload_bio(wc, bio);
    			goto unlock_return;
    		}
    	}
    
    	bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
    
    	if (unlikely((((unsigned)bio->bi_iter.bi_sector | bio_sectors(bio)) &
    				(wc->block_size / 512 - 1)) != 0)) {
    		DMERR("I/O is not aligned, sector %llu, size %u, block size %u",
    		      (unsigned long long)bio->bi_iter.bi_sector,
    		      bio->bi_iter.bi_size, wc->block_size);
    		goto unlock_error;
    	}
    
    	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
    		if (writecache_has_error(wc))
    			goto unlock_error;
    		if (WC_MODE_PMEM(wc)) {
    			writecache_discard(wc, bio->bi_iter.bi_sector, bio_end_sector(bio));
    			goto unlock_remap_origin;
    		} else {
    			writecache_offload_bio(wc, bio);
    			goto unlock_return;
    		}
    	}
    
    	if (bio_data_dir(bio) == READ) {
    read_next_block:
    		e = writecache_find_entry(wc, bio->bi_iter.bi_sector, WFE_RETURN_FOLLOWING);
    		if (e && read_original_sector(wc, e) == bio->bi_iter.bi_sector) {
    			if (WC_MODE_PMEM(wc)) {
    				bio_copy_block(wc, bio, memory_data(wc, e));
    				if (bio->bi_iter.bi_size)
    					goto read_next_block;
    				goto unlock_submit;
    			} else {
    				dm_accept_partial_bio(bio, wc->block_size >> SECTOR_SHIFT);
    				bio_set_dev(bio, wc->ssd_dev->bdev);
    				bio->bi_iter.bi_sector = cache_sector(wc, e);
    				if (!writecache_entry_is_committed(wc, e))
    					writecache_wait_for_ios(wc, WRITE);
    				goto unlock_remap;
    			}
    		} else {
    			if (e) {
    				sector_t next_boundary =
    					read_original_sector(wc, e) - bio->bi_iter.bi_sector;
    				if (next_boundary < bio->bi_iter.bi_size >> SECTOR_SHIFT) {
    					dm_accept_partial_bio(bio, next_boundary);
    				}
    			}
    			goto unlock_remap_origin;
    		}
    	} else {
    		do {
    			bool found_entry = false;
    			if (writecache_has_error(wc))
    				goto unlock_error;
    			e = writecache_find_entry(wc, bio->bi_iter.bi_sector, 0);
    			if (e) {
    				if (!writecache_entry_is_committed(wc, e))
    					goto bio_copy;
    				if (!WC_MODE_PMEM(wc) && !e->write_in_progress) {
    					wc->overwrote_committed = true;
    					goto bio_copy;
    				}
    				found_entry = true;
    			} else {
    				if (unlikely(wc->cleaner))
    					goto direct_write;
    			}
    			e = writecache_pop_from_freelist(wc, (sector_t)-1);
    			if (unlikely(!e)) {
    				if (!found_entry) {
    direct_write:
    					e = writecache_find_entry(wc, bio->bi_iter.bi_sector, WFE_RETURN_FOLLOWING);
    					if (e) {
    						sector_t next_boundary = read_original_sector(wc, e) - bio->bi_iter.bi_sector;
    						BUG_ON(!next_boundary);
    						if (next_boundary < bio->bi_iter.bi_size >> SECTOR_SHIFT) {
    							dm_accept_partial_bio(bio, next_boundary);
    						}
    					}
    					goto unlock_remap_origin;
    				}
    				writecache_wait_on_freelist(wc);
    				continue;
    			}
    			write_original_sector_seq_count(wc, e, bio->bi_iter.bi_sector, wc->seq_count);
    			writecache_insert_entry(wc, e);
    			wc->uncommitted_blocks++;
    bio_copy:
    			if (WC_MODE_PMEM(wc)) {
    				bio_copy_block(wc, bio, memory_data(wc, e));
    			} else {
    				unsigned bio_size = wc->block_size;
    				sector_t start_cache_sec = cache_sector(wc, e);
    				sector_t current_cache_sec = start_cache_sec + (bio_size >> SECTOR_SHIFT);
    
    				while (bio_size < bio->bi_iter.bi_size) {
    					struct wc_entry *f = writecache_pop_from_freelist(wc, current_cache_sec);
    					if (!f)
    						break;
    					write_original_sector_seq_count(wc, f, bio->bi_iter.bi_sector +
    									(bio_size >> SECTOR_SHIFT), wc->seq_count);
    					writecache_insert_entry(wc, f);
    					wc->uncommitted_blocks++;
    					bio_size += wc->block_size;
    					current_cache_sec += wc->block_size >> SECTOR_SHIFT;
    				}
    
    				bio_set_dev(bio, wc->ssd_dev->bdev);
    				bio->bi_iter.bi_sector = start_cache_sec;
    				dm_accept_partial_bio(bio, bio_size >> SECTOR_SHIFT);
    
    				if (unlikely(wc->uncommitted_blocks >= wc->autocommit_blocks)) {
    					wc->uncommitted_blocks = 0;
    					queue_work(wc->writeback_wq, &wc->flush_work);
    				} else {
    					writecache_schedule_autocommit(wc);
    				}
    				goto unlock_remap;
    			}
    		} while (bio->bi_iter.bi_size);
    
    		if (unlikely(bio->bi_opf & REQ_FUA ||
    			     wc->uncommitted_blocks >= wc->autocommit_blocks))
    			writecache_flush(wc);
    		else
    			writecache_schedule_autocommit(wc);
    		goto unlock_submit;
    	}
    
    unlock_remap_origin:
    	bio_set_dev(bio, wc->dev->bdev);
    	wc_unlock(wc);
    	return DM_MAPIO_REMAPPED;
    
    unlock_remap:
    	/* make sure that writecache_end_io decrements bio_in_progress: */
    	bio->bi_private = (void *)1;
    	atomic_inc(&wc->bio_in_progress[bio_data_dir(bio)]);
    	wc_unlock(wc);
    	return DM_MAPIO_REMAPPED;
    
    unlock_submit:
    	wc_unlock(wc);
    	bio_endio(bio);
    	return DM_MAPIO_SUBMITTED;
    
    unlock_return:
    	wc_unlock(wc);
    	return DM_MAPIO_SUBMITTED;
    
    unlock_error:
    	wc_unlock(wc);
    	bio_io_error(bio);
    	return DM_MAPIO_SUBMITTED;
    }
    
    static int writecache_end_io(struct dm_target *ti, struct bio *bio, blk_status_t *status)
    {
    	struct dm_writecache *wc = ti->private;
    
    	if (bio->bi_private != NULL) {
    		int dir = bio_data_dir(bio);
    		if (atomic_dec_and_test(&wc->bio_in_progress[dir]))
    			if (unlikely(waitqueue_active(&wc->bio_in_progress_wait[dir])))
    				wake_up(&wc->bio_in_progress_wait[dir]);
    	}
    	return 0;
    }
    
    static int writecache_iterate_devices(struct dm_target *ti,
    				      iterate_devices_callout_fn fn, void *data)
    {
    	struct dm_writecache *wc = ti->private;
    
    	return fn(ti, wc->dev, 0, ti->len, data);
    }
    
    static void writecache_io_hints(struct dm_target *ti, struct queue_limits *limits)
    {
    	struct dm_writecache *wc = ti->private;
    
    	if (limits->logical_block_size < wc->block_size)
    		limits->logical_block_size = wc->block_size;
    
    	if (limits->physical_block_size < wc->block_size)
    		limits->physical_block_size = wc->block_size;
    
    	if (limits->io_min < wc->block_size)
    		limits->io_min = wc->block_size;
    }
    
    
    static void writecache_writeback_endio(struct bio *bio)
    {
    	struct writeback_struct *wb = container_of(bio, struct writeback_struct, bio);
    	struct dm_writecache *wc = wb->wc;
    	unsigned long flags;
    
    	raw_spin_lock_irqsave(&wc->endio_list_lock, flags);
    	if (unlikely(list_empty(&wc->endio_list)))
    		wake_up_process(wc->endio_thread);
    	list_add_tail(&wb->endio_entry, &wc->endio_list);
    	raw_spin_unlock_irqrestore(&wc->endio_list_lock, flags);
    }
    
    static void writecache_copy_endio(int read_err, unsigned long write_err, void *ptr)
    {
    	struct copy_struct *c = ptr;
    	struct dm_writecache *wc = c->wc;
    
    	c->error = likely(!(read_err | write_err)) ? 0 : -EIO;
    
    	raw_spin_lock_irq(&wc->endio_list_lock);
    	if (unlikely(list_empty(&wc->endio_list)))
    		wake_up_process(wc->endio_thread);
    	list_add_tail(&c->endio_entry, &wc->endio_list);
    	raw_spin_unlock_irq(&wc->endio_list_lock);
    }
    
    static void __writecache_endio_pmem(struct dm_writecache *wc, struct list_head *list)
    {
    	unsigned i;
    	struct writeback_struct *wb;
    	struct wc_entry *e;
    	unsigned long n_walked = 0;
    
    	do {
    		wb = list_entry(list->next, struct writeback_struct, endio_entry);
    		list_del(&wb->endio_entry);
    
    		if (unlikely(wb->bio.bi_status != BLK_STS_OK))
    			writecache_error(wc, blk_status_to_errno(wb->bio.bi_status),
    					"write error %d", wb->bio.bi_status);
    		i = 0;
    		do {
    			e = wb->wc_list[i];
    			BUG_ON(!e->write_in_progress);
    			e->write_in_progress = false;
    			INIT_LIST_HEAD(&e->lru);
    			if (!writecache_has_error(wc))
    				writecache_free_entry(wc, e);
    			BUG_ON(!wc->writeback_size);
    			wc->writeback_size--;
    			n_walked++;
    			if (unlikely(n_walked >= ENDIO_LATENCY)) {
    				writecache_commit_flushed(wc, false);
    				wc_unlock(wc);
    				wc_lock(wc);
    				n_walked = 0;
    			}
    		} while (++i < wb->wc_list_n);
    
    		if (wb->wc_list != wb->wc_list_inline)
    			kfree(wb->wc_list);
    		bio_put(&wb->bio);
    	} while (!list_empty(list));
    }
    
    static void __writecache_endio_ssd(struct dm_writecache *wc, struct list_head *list)
    {
    	struct copy_struct *c;
    	struct wc_entry *e;
    
    	do {
    		c = list_entry(list->next, struct copy_struct, endio_entry);
    		list_del(&c->endio_entry);
    
    		if (unlikely(c->error))
    			writecache_error(wc, c->error, "copy error");
    
    		e = c->e;
    		do {
    			BUG_ON(!e->write_in_progress);
    			e->write_in_progress = false;
    			INIT_LIST_HEAD(&e->lru);
    			if (!writecache_has_error(wc))
    				writecache_free_entry(wc, e);
    
    			BUG_ON(!wc->writeback_size);
    			wc->writeback_size--;
    			e++;
    		} while (--c->n_entries);
    		mempool_free(c, &wc->copy_pool);
    	} while (!list_empty(list));
    }
    
    static int writecache_endio_thread(void *data)
    {
    	struct dm_writecache *wc = data;
    
    	while (1) {
    		struct list_head list;
    
    		raw_spin_lock_irq(&wc->endio_list_lock);
    		if (!list_empty(&wc->endio_list))
    			goto pop_from_list;
    		set_current_state(TASK_INTERRUPTIBLE);
    		raw_spin_unlock_irq(&wc->endio_list_lock);
    
    		if (unlikely(kthread_should_stop())) {
    			set_current_state(TASK_RUNNING);
    			break;
    		}
    
    		schedule();
    
    		continue;
    
    pop_from_list:
    		list = wc->endio_list;
    		list.next->prev = list.prev->next = &list;
    		INIT_LIST_HEAD(&wc->endio_list);
    		raw_spin_unlock_irq(&wc->endio_list_lock);
    
    		if (!WC_MODE_FUA(wc))
    			writecache_disk_flush(wc, wc->dev);
    
    		wc_lock(wc);
    
    		if (WC_MODE_PMEM(wc)) {
    			__writecache_endio_pmem(wc, &list);
    		} else {
    			__writecache_endio_ssd(wc, &list);
    			writecache_wait_for_ios(wc, READ);
    		}
    
    		writecache_commit_flushed(wc, false);
    
    		wc_unlock(wc);
    	}
    
    	return 0;
    }
    
    static bool wc_add_block(struct writeback_struct *wb, struct wc_entry *e, gfp_t gfp)
    {
    	struct dm_writecache *wc = wb->wc;
    	unsigned block_size = wc->block_size;
    	void *address = memory_data(wc, e);
    
    	persistent_memory_flush_cache(address, block_size);
    	return bio_add_page(&wb->bio, persistent_memory_page(address),
    			    block_size, persistent_memory_page_offset(address)) != 0;
    }
    
    struct writeback_list {
    	struct list_head list;
    	size_t size;
    };
    
    static void __writeback_throttle(struct dm_writecache *wc, struct writeback_list *wbl)
    {
    	if (unlikely(wc->max_writeback_jobs)) {
    		if (READ_ONCE(wc->writeback_size) - wbl->size >= wc->max_writeback_jobs) {
    			wc_lock(wc);
    			while (wc->writeback_size - wbl->size >= wc->max_writeback_jobs)
    				writecache_wait_on_freelist(wc);
    			wc_unlock(wc);
    		}
    	}
    	cond_resched();
    }
    
    static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeback_list *wbl)
    {
    	struct wc_entry *e, *f;
    	struct bio *bio;
    	struct writeback_struct *wb;
    	unsigned max_pages;
    
    	while (wbl->size) {
    		wbl->size--;
    		e = container_of(wbl->list.prev, struct wc_entry, lru);
    		list_del(&e->lru);
    
    		max_pages = e->wc_list_contiguous;
    
    		bio = bio_alloc_bioset(GFP_NOIO, max_pages, &wc->bio_set);
    		wb = container_of(bio, struct writeback_struct, bio);
    		wb->wc = wc;
    		bio->bi_end_io = writecache_writeback_endio;
    		bio_set_dev(bio, wc->dev->bdev);
    		bio->bi_iter.bi_sector = read_original_sector(wc, e);
    		if (max_pages <= WB_LIST_INLINE ||
    		    unlikely(!(wb->wc_list = kmalloc_array(max_pages, sizeof(struct wc_entry *),
    							   GFP_NOIO | __GFP_NORETRY |
    							   __GFP_NOMEMALLOC | __GFP_NOWARN)))) {
    			wb->wc_list = wb->wc_list_inline;
    			max_pages = WB_LIST_INLINE;
    		}
    
    		BUG_ON(!wc_add_block(wb, e, GFP_NOIO));
    
    		wb->wc_list[0] = e;
    		wb->wc_list_n = 1;
    
    		while (wbl->size && wb->wc_list_n < max_pages) {
    			f = container_of(wbl->list.prev, struct wc_entry, lru);
    			if (read_original_sector(wc, f) !=
    			    read_original_sector(wc, e) + (wc->block_size >> SECTOR_SHIFT))
    				break;
    			if (!wc_add_block(wb, f, GFP_NOWAIT | __GFP_NOWARN))
    				break;
    			wbl->size--;
    			list_del(&f->lru);
    			wb->wc_list[wb->wc_list_n++] = f;
    			e = f;
    		}
    		bio_set_op_attrs(bio, REQ_OP_WRITE, WC_MODE_FUA(wc) * REQ_FUA);
    		if (writecache_has_error(wc)) {
    			bio->bi_status = BLK_STS_IOERR;
    			bio_endio(bio);
    		} else {
    			submit_bio(bio);
    		}
    
    		__writeback_throttle(wc, wbl);
    	}
    }
    
    static void __writecache_writeback_ssd(struct dm_writecache *wc, struct writeback_list *wbl)
    {
    	struct wc_entry *e, *f;
    	struct dm_io_region from, to;
    	struct copy_struct *c;
    
    	while (wbl->size) {
    		unsigned n_sectors;
    
    		wbl->size--;
    		e = container_of(wbl->list.prev, struct wc_entry, lru);
    		list_del(&e->lru);
    
    		n_sectors = e->wc_list_contiguous << (wc->block_size_bits - SECTOR_SHIFT);
    
    		from.bdev = wc->ssd_dev->bdev;
    		from.sector = cache_sector(wc, e);
    		from.count = n_sectors;
    		to.bdev = wc->dev->bdev;
    		to.sector = read_original_sector(wc, e);
    		to.count = n_sectors;
    
    		c = mempool_alloc(&wc->copy_pool, GFP_NOIO);
    		c->wc = wc;
    		c->e = e;
    		c->n_entries = e->wc_list_contiguous;
    
    		while ((n_sectors -= wc->block_size >> SECTOR_SHIFT)) {
    			wbl->size--;
    			f = container_of(wbl->list.prev, struct wc_entry, lru);
    			BUG_ON(f != e + 1);
    			list_del(&f->lru);
    			e = f;
    		}
    
    		dm_kcopyd_copy(wc->dm_kcopyd, &from, 1, &to, 0, writecache_copy_endio, c);
    
    		__writeback_throttle(wc, wbl);
    	}
    }
    
    static void writecache_writeback(struct work_struct *work)
    {
    	struct dm_writecache *wc = container_of(work, struct dm_writecache, writeback_work);
    	struct blk_plug plug;
    	struct wc_entry *f, *uninitialized_var(g), *e = NULL;
    	struct rb_node *node, *next_node;
    	struct list_head skipped;
    	struct writeback_list wbl;
    	unsigned long n_walked;
    
    	wc_lock(wc);
    restart:
    	if (writecache_has_error(wc)) {
    		wc_unlock(wc);
    		return;
    	}
    
    	if (unlikely(wc->writeback_all)) {
    		if (writecache_wait_for_writeback(wc))
    			goto restart;
    	}
    
    	if (wc->overwrote_committed) {
    		writecache_wait_for_ios(wc, WRITE);
    	}
    
    	n_walked = 0;
    	INIT_LIST_HEAD(&skipped);
    	INIT_LIST_HEAD(&wbl.list);
    	wbl.size = 0;
    	while (!list_empty(&wc->lru) &&
    	       (wc->writeback_all ||
    		wc->freelist_size + wc->writeback_size <= wc->freelist_low_watermark ||
    		(jiffies - container_of(wc->lru.prev, struct wc_entry, lru)->age >=
    		 wc->max_age - wc->max_age / MAX_AGE_DIV))) {
    
    		n_walked++;
    		if (unlikely(n_walked > WRITEBACK_LATENCY) &&
    		    likely(!wc->writeback_all) && likely(!dm_suspended(wc->ti))) {
    			queue_work(wc->writeback_wq, &wc->writeback_work);
    			break;
    		}
    
    		if (unlikely(wc->writeback_all)) {
    			if (unlikely(!e)) {
    				writecache_flush(wc);
    				e = container_of(rb_first(&wc->tree), struct wc_entry, rb_node);
    			} else
    				e = g;
    		} else
    			e = container_of(wc->lru.prev, struct wc_entry, lru);
    		BUG_ON(e->write_in_progress);
    		if (unlikely(!writecache_entry_is_committed(wc, e))) {
    			writecache_flush(wc);
    		}
    		node = rb_prev(&e->rb_node);
    		if (node) {
    			f = container_of(node, struct wc_entry, rb_node);
    			if (unlikely(read_original_sector(wc, f) ==
    				     read_original_sector(wc, e))) {
    				BUG_ON(!f->write_in_progress);
    				list_del(&e->lru);
    				list_add(&e->lru, &skipped);
    				cond_resched();
    				continue;
    			}
    		}
    		wc->writeback_size++;
    		list_del(&e->lru);
    		list_add(&e->lru, &wbl.list);
    		wbl.size++;
    		e->write_in_progress = true;
    		e->wc_list_contiguous = 1;
    
    		f = e;
    
    		while (1) {
    			next_node = rb_next(&f->rb_node);
    			if (unlikely(!next_node))
    				break;
    			g = container_of(next_node, struct wc_entry, rb_node);
    			if (unlikely(read_original_sector(wc, g) ==
    			    read_original_sector(wc, f))) {
    				f = g;
    				continue;
    			}
    			if (read_original_sector(wc, g) !=
    			    read_original_sector(wc, f) + (wc->block_size >> SECTOR_SHIFT))
    				break;
    			if (unlikely(g->write_in_progress))
    				break;
    			if (unlikely(!writecache_entry_is_committed(wc, g)))
    				break;
    
    			if (!WC_MODE_PMEM(wc)) {
    				if (g != f + 1)
    					break;
    			}
    
    			n_walked++;
    			//if (unlikely(n_walked > WRITEBACK_LATENCY) && likely(!wc->writeback_all))
    			//	break;
    
    			wc->writeback_size++;
    			list_del(&g->lru);
    			list_add(&g->lru, &wbl.list);
    			wbl.size++;
    			g->write_in_progress = true;
    			g->wc_list_contiguous = BIO_MAX_PAGES;
    			f = g;
    			e->wc_list_contiguous++;
    			if (unlikely(e->wc_list_contiguous == BIO_MAX_PAGES)) {
    				if (unlikely(wc->writeback_all)) {
    					next_node = rb_next(&f->rb_node);
    					if (likely(next_node))
    						g = container_of(next_node, struct wc_entry, rb_node);
    				}
    				break;
    			}
    		}
    		cond_resched();
    	}
    
    	if (!list_empty(&skipped)) {
    		list_splice_tail(&skipped, &wc->lru);
    		/*
    		 * If we didn't do any progress, we must wait until some
    		 * writeback finishes to avoid burning CPU in a loop
    		 */
    		if (unlikely(!wbl.size))
    			writecache_wait_for_writeback(wc);
    	}
    
    	wc_unlock(wc);
    
    	blk_start_plug(&plug);
    
    	if (WC_MODE_PMEM(wc))
    		__writecache_writeback_pmem(wc, &wbl);
    	else
    		__writecache_writeback_ssd(wc, &wbl);
    
    	blk_finish_plug(&plug);
    
    	if (unlikely(wc->writeback_all)) {
    		wc_lock(wc);
    		while (writecache_wait_for_writeback(wc));
    		wc_unlock(wc);
    	}
    }
    
    static int calculate_memory_size(uint64_t device_size, unsigned block_size,
    				 size_t *n_blocks_p, size_t *n_metadata_blocks_p)
    {
    	uint64_t n_blocks, offset;
    	struct wc_entry e;
    
    	n_blocks = device_size;
    	do_div(n_blocks, block_size + sizeof(struct wc_memory_entry));
    
    	while (1) {
    		if (!n_blocks)
    			return -ENOSPC;
    		/* Verify the following entries[n_blocks] won't overflow */
    		if (n_blocks >= ((size_t)-sizeof(struct wc_memory_superblock) /
    				 sizeof(struct wc_memory_entry)))
    			return -EFBIG;
    		offset = offsetof(struct wc_memory_superblock, entries[n_blocks]);
    		offset = (offset + block_size - 1) & ~(uint64_t)(block_size - 1);
    		if (offset + n_blocks * block_size <= device_size)
    			break;
    		n_blocks--;
    	}
    
    	/* check if the bit field overflows */
    	e.index = n_blocks;
    	if (e.index != n_blocks)
    		return -EFBIG;
    
    	if (n_blocks_p)
    		*n_blocks_p = n_blocks;
    	if (n_metadata_blocks_p)
    		*n_metadata_blocks_p = offset >> __ffs(block_size);
    	return 0;
    }
    
    static int init_memory(struct dm_writecache *wc)
    {
    	size_t b;
    	int r;
    
    	r = calculate_memory_size(wc->memory_map_size, wc->block_size, &wc->n_blocks, NULL);
    	if (r)
    		return r;
    
    	r = writecache_alloc_entries(wc);
    	if (r)
    		return r;
    
    	for (b = 0; b < ARRAY_SIZE(sb(wc)->padding); b++)
    		pmem_assign(sb(wc)->padding[b], cpu_to_le64(0));
    	pmem_assign(sb(wc)->version, cpu_to_le32(MEMORY_SUPERBLOCK_VERSION));
    	pmem_assign(sb(wc)->block_size, cpu_to_le32(wc->block_size));
    	pmem_assign(sb(wc)->n_blocks, cpu_to_le64(wc->n_blocks));
    	pmem_assign(sb(wc)->seq_count, cpu_to_le64(0));
    
    	for (b = 0; b < wc->n_blocks; b++)
    		write_original_sector_seq_count(wc, &wc->entries[b], -1, -1);
    
    	writecache_flush_all_metadata(wc);
    	writecache_commit_flushed(wc, false);
    	pmem_assign(sb(wc)->magic, cpu_to_le32(MEMORY_SUPERBLOCK_MAGIC));
    	writecache_flush_region(wc, &sb(wc)->magic, sizeof sb(wc)->magic);
    	writecache_commit_flushed(wc, false);
    
    	return 0;
    }
    
    static void writecache_dtr(struct dm_target *ti)
    {
    	struct dm_writecache *wc = ti->private;
    
    	if (!wc)
    		return;
    
    	if (wc->endio_thread)
    		kthread_stop(wc->endio_thread);
    
    	if (wc->flush_thread)
    		kthread_stop(wc->flush_thread);
    
    	bioset_exit(&wc->bio_set);
    
    	mempool_exit(&wc->copy_pool);
    
    	if (wc->writeback_wq)
    		destroy_workqueue(wc->writeback_wq);
    
    	if (wc->dev)
    		dm_put_device(ti, wc->dev);
    
    	if (wc->ssd_dev)
    		dm_put_device(ti, wc->ssd_dev);
    
    	if (wc->entries)
    		vfree(wc->entries);
    
    	if (wc->memory_map) {
    		if (WC_MODE_PMEM(wc))
    			persistent_memory_release(wc);
    		else
    			vfree(wc->memory_map);
    	}
    
    	if (wc->dm_kcopyd)
    		dm_kcopyd_client_destroy(wc->dm_kcopyd);
    
    	if (wc->dm_io)
    		dm_io_client_destroy(wc->dm_io);
    
    	if (wc->dirty_bitmap)
    		vfree(wc->dirty_bitmap);
    
    	kfree(wc);
    }
    
    static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
    {
    	struct dm_writecache *wc;
    	struct dm_arg_set as;
    	const char *string;
    	unsigned opt_params;
    	size_t offset, data_size;
    	int i, r;
    	char dummy;
    	int high_wm_percent = HIGH_WATERMARK;
    	int low_wm_percent = LOW_WATERMARK;
    	uint64_t x;
    	struct wc_memory_superblock s;
    
    	static struct dm_arg _args[] = {
    		{0, 10, "Invalid number of feature args"},
    	};
    
    	as.argc = argc;
    	as.argv = argv;
    
    	wc = kzalloc(sizeof(struct dm_writecache), GFP_KERNEL);
    	if (!wc) {
    		ti->error = "Cannot allocate writecache structure";
    		r = -ENOMEM;
    		goto bad;
    	}
    	ti->private = wc;
    	wc->ti = ti;
    
    	mutex_init(&wc->lock);
    	wc->max_age = MAX_AGE_UNSPECIFIED;
    	writecache_poison_lists(wc);
    	init_waitqueue_head(&wc->freelist_wait);
    	timer_setup(&wc->autocommit_timer, writecache_autocommit_timer, 0);
    	timer_setup(&wc->max_age_timer, writecache_max_age_timer, 0);
    
    	for (i = 0; i < 2; i++) {
    		atomic_set(&wc->bio_in_progress[i], 0);
    		init_waitqueue_head(&wc->bio_in_progress_wait[i]);
    	}
    
    	wc->dm_io = dm_io_client_create();
    	if (IS_ERR(wc->dm_io)) {
    		r = PTR_ERR(wc->dm_io);
    		ti->error = "Unable to allocate dm-io client";
    		wc->dm_io = NULL;
    		goto bad;
    	}
    
    	wc->writeback_wq = alloc_workqueue("writecache-writeback", WQ_MEM_RECLAIM, 1);
    	if (!wc->writeback_wq) {
    		r = -ENOMEM;
    		ti->error = "Could not allocate writeback workqueue";
    		goto bad;
    	}
    	INIT_WORK(&wc->writeback_work, writecache_writeback);
    	INIT_WORK(&wc->flush_work, writecache_flush_work);
    
    	raw_spin_lock_init(&wc->endio_list_lock);
    	INIT_LIST_HEAD(&wc->endio_list);
    	wc->endio_thread = kthread_create(writecache_endio_thread, wc, "writecache_endio");
    	if (IS_ERR(wc->endio_thread)) {
    		r = PTR_ERR(wc->endio_thread);
    		wc->endio_thread = NULL;
    		ti->error = "Couldn't spawn endio thread";
    		goto bad;
    	}
    	wake_up_process(wc->endio_thread);
    
    	/*
    	 * Parse the mode (pmem or ssd)
    	 */
    	string = dm_shift_arg(&as);
    	if (!string)
    		goto bad_arguments;
    
    	if (!strcasecmp(string, "s")) {
    		wc->pmem_mode = false;
    	} else if (!strcasecmp(string, "p")) {
    #ifdef DM_WRITECACHE_HAS_PMEM
    		wc->pmem_mode = true;
    		wc->writeback_fua = true;
    #else
    		/*
    		 * If the architecture doesn't support persistent memory or
    		 * the kernel doesn't support any DAX drivers, this driver can
    		 * only be used in SSD-only mode.
    		 */
    		r = -EOPNOTSUPP;
    		ti->error = "Persistent memory or DAX not supported on this system";
    		goto bad;
    #endif
    	} else {
    		goto bad_arguments;
    	}
    
    	if (WC_MODE_PMEM(wc)) {
    		r = bioset_init(&wc->bio_set, BIO_POOL_SIZE,
    				offsetof(struct writeback_struct, bio),
    				BIOSET_NEED_BVECS);
    		if (r) {
    			ti->error = "Could not allocate bio set";
    			goto bad;
    		}
    	} else {
    		r = mempool_init_kmalloc_pool(&wc->copy_pool, 1, sizeof(struct copy_struct));
    		if (r) {
    			ti->error = "Could not allocate mempool";
    			goto bad;
    		}
    	}
    
    	/*
    	 * Parse the origin data device
    	 */
    	string = dm_shift_arg(&as);
    	if (!string)
    		goto bad_arguments;
    	r = dm_get_device(ti, string, dm_table_get_mode(ti->table), &wc->dev);
    	if (r) {
    		ti->error = "Origin data device lookup failed";
    		goto bad;
    	}
    
    	/*
    	 * Parse cache data device (be it pmem or ssd)
    	 */
    	string = dm_shift_arg(&as);
    	if (!string)
    		goto bad_arguments;
    
    	r = dm_get_device(ti, string, dm_table_get_mode(ti->table), &wc->ssd_dev);
    	if (r) {
    		ti->error = "Cache data device lookup failed";
    		goto bad;
    	}
    	wc->memory_map_size = i_size_read(wc->ssd_dev->bdev->bd_inode);
    
    	/*
    	 * Parse the cache block size
    	 */
    	string = dm_shift_arg(&as);
    	if (!string)
    		goto bad_arguments;
    	if (sscanf(string, "%u%c", &wc->block_size, &dummy) != 1 ||
    	    wc->block_size < 512 || wc->block_size > PAGE_SIZE ||
    	    (wc->block_size & (wc->block_size - 1))) {
    		r = -EINVAL;
    		ti->error = "Invalid block size";
    		goto bad;
    	}
    	wc->block_size_bits = __ffs(wc->block_size);
    
    	wc->max_writeback_jobs = MAX_WRITEBACK_JOBS;
    	wc->autocommit_blocks = !WC_MODE_PMEM(wc) ? AUTOCOMMIT_BLOCKS_SSD : AUTOCOMMIT_BLOCKS_PMEM;
    	wc->autocommit_jiffies = msecs_to_jiffies(AUTOCOMMIT_MSEC);
    
    	/*
    	 * Parse optional arguments
    	 */
    	r = dm_read_arg_group(_args, &as, &opt_params, &ti->error);
    	if (r)
    		goto bad;
    
    	while (opt_params) {
    		string = dm_shift_arg(&as), opt_params--;
    		if (!strcasecmp(string, "start_sector") && opt_params >= 1) {
    			unsigned long long start_sector;
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%llu%c", &start_sector, &dummy) != 1)
    				goto invalid_optional;
    			wc->start_sector = start_sector;
    			if (wc->start_sector != start_sector ||
    			    wc->start_sector >= wc->memory_map_size >> SECTOR_SHIFT)
    				goto invalid_optional;
    		} else if (!strcasecmp(string, "high_watermark") && opt_params >= 1) {
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%d%c", &high_wm_percent, &dummy) != 1)
    				goto invalid_optional;
    			if (high_wm_percent < 0 || high_wm_percent > 100)
    				goto invalid_optional;
    			wc->high_wm_percent_set = true;
    		} else if (!strcasecmp(string, "low_watermark") && opt_params >= 1) {
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%d%c", &low_wm_percent, &dummy) != 1)
    				goto invalid_optional;
    			if (low_wm_percent < 0 || low_wm_percent > 100)
    				goto invalid_optional;
    			wc->low_wm_percent_set = true;
    		} else if (!strcasecmp(string, "writeback_jobs") && opt_params >= 1) {
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%u%c", &wc->max_writeback_jobs, &dummy) != 1)
    				goto invalid_optional;
    			wc->max_writeback_jobs_set = true;
    		} else if (!strcasecmp(string, "autocommit_blocks") && opt_params >= 1) {
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%u%c", &wc->autocommit_blocks, &dummy) != 1)
    				goto invalid_optional;
    			wc->autocommit_blocks_set = true;
    		} else if (!strcasecmp(string, "autocommit_time") && opt_params >= 1) {
    			unsigned autocommit_msecs;
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%u%c", &autocommit_msecs, &dummy) != 1)
    				goto invalid_optional;
    			if (autocommit_msecs > 3600000)
    				goto invalid_optional;
    			wc->autocommit_jiffies = msecs_to_jiffies(autocommit_msecs);
    			wc->autocommit_time_set = true;
    		} else if (!strcasecmp(string, "max_age") && opt_params >= 1) {
    			unsigned max_age_msecs;
    			string = dm_shift_arg(&as), opt_params--;
    			if (sscanf(string, "%u%c", &max_age_msecs, &dummy) != 1)
    				goto invalid_optional;
    			if (max_age_msecs > 86400000)
    				goto invalid_optional;
    			wc->max_age = msecs_to_jiffies(max_age_msecs);
    		} else if (!strcasecmp(string, "cleaner")) {
    			wc->cleaner = true;
    		} else if (!strcasecmp(string, "fua")) {
    			if (WC_MODE_PMEM(wc)) {
    				wc->writeback_fua = true;
    				wc->writeback_fua_set = true;
    			} else goto invalid_optional;
    		} else if (!strcasecmp(string, "nofua")) {
    			if (WC_MODE_PMEM(wc)) {
    				wc->writeback_fua = false;
    				wc->writeback_fua_set = true;
    			} else goto invalid_optional;
    		} else {
    invalid_optional:
    			r = -EINVAL;
    			ti->error = "Invalid optional argument";
    			goto bad;
    		}
    	}
    
    	if (high_wm_percent < low_wm_percent) {
    		r = -EINVAL;
    		ti->error = "High watermark must be greater than or equal to low watermark";
    		goto bad;
    	}
    
    	if (WC_MODE_PMEM(wc)) {
    		r = persistent_memory_claim(wc);
    		if (r) {
    			ti->error = "Unable to map persistent memory for cache";
    			goto bad;
    		}
    	} else {
    		struct dm_io_region region;
    		struct dm_io_request req;
    		size_t n_blocks, n_metadata_blocks;
    		uint64_t n_bitmap_bits;
    
    		wc->memory_map_size -= (uint64_t)wc->start_sector << SECTOR_SHIFT;
    
    		bio_list_init(&wc->flush_list);
    		wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush");
    		if (IS_ERR(wc->flush_thread)) {
    			r = PTR_ERR(wc->flush_thread);
    			wc->flush_thread = NULL;
    			ti->error = "Couldn't spawn flush thread";
    			goto bad;
    		}
    		wake_up_process(wc->flush_thread);
    
    		r = calculate_memory_size(wc->memory_map_size, wc->block_size,
    					  &n_blocks, &n_metadata_blocks);
    		if (r) {
    			ti->error = "Invalid device size";
    			goto bad;
    		}
    
    		n_bitmap_bits = (((uint64_t)n_metadata_blocks << wc->block_size_bits) +
    				 BITMAP_GRANULARITY - 1) / BITMAP_GRANULARITY;
    		/* this is limitation of test_bit functions */
    		if (n_bitmap_bits > 1U << 31) {
    			r = -EFBIG;
    			ti->error = "Invalid device size";
    			goto bad;
    		}
    
    		wc->memory_map = vmalloc(n_metadata_blocks << wc->block_size_bits);
    		if (!wc->memory_map) {
    			r = -ENOMEM;
    			ti->error = "Unable to allocate memory for metadata";
    			goto bad;
    		}
    
    		wc->dm_kcopyd = dm_kcopyd_client_create(&dm_kcopyd_throttle);
    		if (IS_ERR(wc->dm_kcopyd)) {
    			r = PTR_ERR(wc->dm_kcopyd);
    			ti->error = "Unable to allocate dm-kcopyd client";
    			wc->dm_kcopyd = NULL;
    			goto bad;
    		}
    
    		wc->metadata_sectors = n_metadata_blocks << (wc->block_size_bits - SECTOR_SHIFT);
    		wc->dirty_bitmap_size = (n_bitmap_bits + BITS_PER_LONG - 1) /
    			BITS_PER_LONG * sizeof(unsigned long);
    		wc->dirty_bitmap = vzalloc(wc->dirty_bitmap_size);
    		if (!wc->dirty_bitmap) {
    			r = -ENOMEM;
    			ti->error = "Unable to allocate dirty bitmap";
    			goto bad;
    		}
    
    		region.bdev = wc->ssd_dev->bdev;
    		region.sector = wc->start_sector;
    		region.count = wc->metadata_sectors;
    		req.bi_op = REQ_OP_READ;
    		req.bi_op_flags = REQ_SYNC;
    		req.mem.type = DM_IO_VMA;
    		req.mem.ptr.vma = (char *)wc->memory_map;
    		req.client = wc->dm_io;
    		req.notify.fn = NULL;
    
    		r = dm_io(&req, 1, &region, NULL);
    		if (r) {
    			ti->error = "Unable to read metadata";
    			goto bad;
    		}
    	}
    
    	r = memcpy_mcsafe(&s, sb(wc), sizeof(struct wc_memory_superblock));
    	if (r) {
    		ti->error = "Hardware memory error when reading superblock";
    		goto bad;
    	}
    	if (!le32_to_cpu(s.magic) && !le32_to_cpu(s.version)) {
    		r = init_memory(wc);
    		if (r) {
    			ti->error = "Unable to initialize device";
    			goto bad;
    		}
    		r = memcpy_mcsafe(&s, sb(wc), sizeof(struct wc_memory_superblock));
    		if (r) {
    			ti->error = "Hardware memory error when reading superblock";
    			goto bad;
    		}
    	}
    
    	if (le32_to_cpu(s.magic) != MEMORY_SUPERBLOCK_MAGIC) {
    		ti->error = "Invalid magic in the superblock";
    		r = -EINVAL;
    		goto bad;
    	}
    
    	if (le32_to_cpu(s.version) != MEMORY_SUPERBLOCK_VERSION) {
    		ti->error = "Invalid version in the superblock";
    		r = -EINVAL;
    		goto bad;
    	}
    
    	if (le32_to_cpu(s.block_size) != wc->block_size) {
    		ti->error = "Block size does not match superblock";
    		r = -EINVAL;
    		goto bad;
    	}
    
    	wc->n_blocks = le64_to_cpu(s.n_blocks);
    
    	offset = wc->n_blocks * sizeof(struct wc_memory_entry);
    	if (offset / sizeof(struct wc_memory_entry) != le64_to_cpu(sb(wc)->n_blocks)) {
    overflow:
    		ti->error = "Overflow in size calculation";
    		r = -EINVAL;
    		goto bad;
    	}
    	offset += sizeof(struct wc_memory_superblock);
    	if (offset < sizeof(struct wc_memory_superblock))
    		goto overflow;
    	offset = (offset + wc->block_size - 1) & ~(size_t)(wc->block_size - 1);
    	data_size = wc->n_blocks * (size_t)wc->block_size;
    	if (!offset || (data_size / wc->block_size != wc->n_blocks) ||
    	    (offset + data_size < offset))
    		goto overflow;
    	if (offset + data_size > wc->memory_map_size) {
    		ti->error = "Memory area is too small";
    		r = -EINVAL;
    		goto bad;
    	}
    
    	wc->metadata_sectors = offset >> SECTOR_SHIFT;
    	wc->block_start = (char *)sb(wc) + offset;
    
    	x = (uint64_t)wc->n_blocks * (100 - high_wm_percent);
    	x += 50;
    	do_div(x, 100);
    	wc->freelist_high_watermark = x;
    	x = (uint64_t)wc->n_blocks * (100 - low_wm_percent);
    	x += 50;
    	do_div(x, 100);
    	wc->freelist_low_watermark = x;
    
    	if (wc->cleaner)
    		activate_cleaner(wc);
    
    	r = writecache_alloc_entries(wc);
    	if (r) {
    		ti->error = "Cannot allocate memory";
    		goto bad;
    	}
    
    	ti->num_flush_bios = 1;
    	ti->flush_supported = true;
    	ti->num_discard_bios = 1;
    
    	if (WC_MODE_PMEM(wc))
    		persistent_memory_flush_cache(wc->memory_map, wc->memory_map_size);
    
    	return 0;
    
    bad_arguments:
    	r = -EINVAL;
    	ti->error = "Bad arguments";
    bad:
    	writecache_dtr(ti);
    	return r;
    }
    
    static void writecache_status(struct dm_target *ti, status_type_t type,
    			      unsigned status_flags, char *result, unsigned maxlen)
    {
    	struct dm_writecache *wc = ti->private;
    	unsigned extra_args;
    	unsigned sz = 0;
    	uint64_t x;
    
    	switch (type) {
    	case STATUSTYPE_INFO:
    		DMEMIT("%ld %llu %llu %llu", writecache_has_error(wc),
    		       (unsigned long long)wc->n_blocks, (unsigned long long)wc->freelist_size,
    		       (unsigned long long)wc->writeback_size);
    		break;
    	case STATUSTYPE_TABLE:
    		DMEMIT("%c %s %s %u ", WC_MODE_PMEM(wc) ? 'p' : 's',
    				wc->dev->name, wc->ssd_dev->name, wc->block_size);
    		extra_args = 0;
    		if (wc->start_sector)
    			extra_args += 2;
    		if (wc->high_wm_percent_set && !wc->cleaner)
    			extra_args += 2;
    		if (wc->low_wm_percent_set && !wc->cleaner)
    			extra_args += 2;
    		if (wc->max_writeback_jobs_set)
    			extra_args += 2;
    		if (wc->autocommit_blocks_set)
    			extra_args += 2;
    		if (wc->autocommit_time_set)
    			extra_args += 2;
    		if (wc->cleaner)
    			extra_args++;
    		if (wc->writeback_fua_set)
    			extra_args++;
    
    		DMEMIT("%u", extra_args);
    		if (wc->start_sector)
    			DMEMIT(" start_sector %llu", (unsigned long long)wc->start_sector);
    		if (wc->high_wm_percent_set && !wc->cleaner) {
    			x = (uint64_t)wc->freelist_high_watermark * 100;
    			x += wc->n_blocks / 2;
    			do_div(x, (size_t)wc->n_blocks);
    			DMEMIT(" high_watermark %u", 100 - (unsigned)x);
    		}
    		if (wc->low_wm_percent_set && !wc->cleaner) {
    			x = (uint64_t)wc->freelist_low_watermark * 100;
    			x += wc->n_blocks / 2;
    			do_div(x, (size_t)wc->n_blocks);
    			DMEMIT(" low_watermark %u", 100 - (unsigned)x);
    		}
    		if (wc->max_writeback_jobs_set)
    			DMEMIT(" writeback_jobs %u", wc->max_writeback_jobs);
    		if (wc->autocommit_blocks_set)
    			DMEMIT(" autocommit_blocks %u", wc->autocommit_blocks);
    		if (wc->autocommit_time_set)
    			DMEMIT(" autocommit_time %u", jiffies_to_msecs(wc->autocommit_jiffies));
    		if (wc->max_age != MAX_AGE_UNSPECIFIED)
    			DMEMIT(" max_age %u", jiffies_to_msecs(wc->max_age));
    		if (wc->cleaner)
    			DMEMIT(" cleaner");
    		if (wc->writeback_fua_set)
    			DMEMIT(" %sfua", wc->writeback_fua ? "" : "no");
    		break;
    	}
    }
    
    static struct target_type writecache_target = {
    	.name			= "writecache",
    	.version		= {1, 3, 0},
    	.module			= THIS_MODULE,
    	.ctr			= writecache_ctr,
    	.dtr			= writecache_dtr,
    	.status			= writecache_status,
    	.postsuspend		= writecache_suspend,
    	.resume			= writecache_resume,
    	.message		= writecache_message,
    	.map			= writecache_map,
    	.end_io			= writecache_end_io,
    	.iterate_devices	= writecache_iterate_devices,
    	.io_hints		= writecache_io_hints,
    };
    
    static int __init dm_writecache_init(void)
    {
    	int r;
    
    	r = dm_register_target(&writecache_target);
    	if (r < 0) {
    		DMERR("register failed %d", r);
    		return r;
    	}
    
    	return 0;
    }
    
    static void __exit dm_writecache_exit(void)
    {
    	dm_unregister_target(&writecache_target);
    }
    
    module_init(dm_writecache_init);
    module_exit(dm_writecache_exit);
    
    MODULE_DESCRIPTION(DM_NAME " writecache target");
    MODULE_AUTHOR("Mikulas Patocka <dm-devel@redhat.com>");
    MODULE_LICENSE("GPL");