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Gmane
From: <clinew <at> linux.vnet.ibm.com>
Subject: [PATCH] [RFC v2] Btrfs: Subpagesize blocksize (WIP).
Newsgroups: gmane.comp.file-systems.btrfs
Date: Tuesday 18th December 2012 07:13:25 UTC (over 5 years ago)
From: Wade Cline 

v1 -> v2:
- Added Signed-off-by tag (it's kind of important).

This patch is only an RFC. My internship is ending and I was hoping
to get some feedback and incorporate any suggestions people may
have before my internship ends along with life as we know it (this
Friday).

The filesystem should mount/umount properly but tends towards the
explosive side when writes start happening. My current focus is on
checksumming issues and also an error when releasing extent buffers
when creating a large file with 'dd'... and probably any other
method. There's still a significant amount of work that needs to be
done before this should be incorporated into mainline.

A couple of notes:
    - Based off of Josef's btrfs-next branch, commit
      8d089a86e45b34d7bc534d955e9d8543609f7e42
    - C99-style comments are "meta-comments" where I'd like more
      feedback; they aren't permanent but make 'checkpatch' moan.
    - extent_buffer allocation and freeing need their code paths
      merged; they're currently in separate functions and are both
      very ugly.
    - The patch itself will eventually need to be broken down
      into smaller pieces if at all possible...

Signed-off-by: Wade Cline 
---
 fs/btrfs/ctree.h            |   11 +-
 fs/btrfs/disk-io.c          |  110 +++++++--
 fs/btrfs/extent_io.c        |  632
++++++++++++++++++++++++++++++++++++++-----
 fs/btrfs/extent_io.h        |    7 +
 fs/btrfs/file.c             |    9 +-
 fs/btrfs/free-space-cache.c |    2 +
 fs/btrfs/inode.c            |   38 ++-
 fs/btrfs/ioctl.c            |    4 +-
 8 files changed, 709 insertions(+), 104 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index fbaaf20..c786a58 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1938,14 +1938,19 @@ static inline void btrfs_set_token_##name(struct
extent_buffer *eb,	\
 #define BTRFS_SETGET_HEADER_FUNCS(name, type, member, bits)		\
 static inline u##bits btrfs_##name(struct extent_buffer *eb)		\
 {									\
-	type *p = page_address(eb->pages[0]);				\
-	u##bits res = le##bits##_to_cpu(p->member);			\
+	type *p;							\
+	u##bits res;							\
+									\
+	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
+	res = le##bits##_to_cpu(p->member);				\
 	return res;							\
 }									\
 static inline void btrfs_set_##name(struct extent_buffer *eb,		\
 				    u##bits val)			\
 {									\
-	type *p = page_address(eb->pages[0]);				\
+	type *p;							\
+									\
+	p = page_address(eb->pages[0]) + (eb->start & (PAGE_SIZE - 1)); \
 	p->member = cpu_to_le##bits(val);				\
 }
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f633af8..00b80b7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -373,6 +373,24 @@ static int btree_read_extent_buffer_pages(struct
btrfs_root *root,
 					       WAIT_COMPLETE,
 					       btree_get_extent, mirror_num);
 		if (!ret) {
+			/*
+			 * I think that this is bad and should be moved
+			 * into btree_readpage_end_io_hook(), but that
+			 * it should apply to a single block at a time.
+			 * That may be difficult and would make the
+			 * function name a misnomer, but mostly I hate
+			 * the silly goto.
+			 */
+			if (eb->len < PAGE_SIZE &&
+			    !extent_buffer_uptodate(eb)) {
+				if (csum_tree_block(root, eb, 1)) {
+					ret = -EIO;
+					goto bad;
+				} else {
+					set_extent_buffer_uptodate(eb);
+				}
+			}
+
 			if (!verify_parent_transid(io_tree, eb,
 						   parent_transid, 0))
 				break;
@@ -385,6 +403,7 @@ static int btree_read_extent_buffer_pages(struct
btrfs_root *root,
 		 * there is no reason to read the other copies, they won't be
 		 * any less wrong.
 		 */
+bad:
 		if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
 			break;
 
@@ -416,29 +435,55 @@ static int btree_read_extent_buffer_pages(struct
btrfs_root *root,
  * checksum a dirty tree block before IO.  This has extra checks to make
sure
  * we only fill in the checksum field in the first page of a multi-page
block
  */
-
-static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
+static int csum_dirty_buffer(struct btrfs_root *root, struct page *page,
+			     unsigned int offset, unsigned int len)
 {
-	struct extent_io_tree *tree;
 	u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
 	u64 found_start;
 	struct extent_buffer *eb;
 
-	tree = &BTRFS_I(page->mapping->host)->io_tree;
+	if (!PageUptodate(page)) {
+		WARN_ON(1);
+		return 0;
+	}
 
 	eb = (struct extent_buffer *)page->private;
-	if (page != eb->pages[0])
-		return 0;
+	if (eb->len >= PAGE_SIZE) {
+		if (eb->pages[0] != page)
+			return 0;
+	} else {
+		start += offset;
+		while (eb->start != start) {
+			eb = eb->next;
+			BUG_ON(!eb);
+		}
+next:
+		if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+			WARN_ON(1);
+		if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
+			WARN_ON(1);
+		if (eb->pages[0] != page)
+			WARN_ON(1);
+	}
+
 	found_start = btrfs_header_bytenr(eb);
 	if (found_start != start) {
 		WARN_ON(1);
 		return 0;
 	}
-	if (!PageUptodate(page)) {
-		WARN_ON(1);
-		return 0;
-	}
+
 	csum_tree_block(root, eb, 0);
+
+	if (eb->len < PAGE_SIZE) {
+		len -= eb->len;
+		BUG_ON(len & (eb->len - 1));
+		if (len) {
+			start += eb->len;
+			eb = eb->next;
+			goto next;
+		}
+	}
+
 	return 0;
 }
 
@@ -579,6 +624,19 @@ static int btree_readpage_end_io_hook(struct page
*page, u64 start, u64 end,
 
 	tree = &BTRFS_I(page->mapping->host)->io_tree;
 	eb = (struct extent_buffer *)page->private;
+	if (eb->len < PAGE_SIZE) {
+		/* Find the eb that tried to submit a read request. This is
+		 * a little bit funky. */
+		do {
+			if (!atomic_read(&eb->io_pages))
+				continue;
+			if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags) ||
+			    test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+				continue;
+			break;
+		} while ((eb = eb->next));
+		BUG_ON(!eb);
+	}
 
 	/* the pending IO might have been the only thing that kept this buffer
 	 * in memory.  Make sure we have a ref for all this other checks
@@ -615,8 +673,11 @@ static int btree_readpage_end_io_hook(struct page
*page, u64 start, u64 end,
 	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb),
 				       eb, found_level);
 
-	ret = csum_tree_block(root, eb, 1);
-	if (ret) {
+	/*
+	 * Subpagesize blocksize checksumming is currently done in
+	 * btree_read_extent_buffer_pages().
+	 */
+	if (eb->len >= PAGE_SIZE && csum_tree_block(root, eb, 1)) {
 		ret = -EIO;
 		goto err;
 	}
@@ -631,8 +692,15 @@ static int btree_readpage_end_io_hook(struct page
*page, u64 start, u64 end,
 		ret = -EIO;
 	}
 
-	if (!ret)
+	/*
+	 * For subpagesize blocksize, only the page needs to be set
+	 * up-to-date; each extent_buffer is set up-to-date when it is
+	 * checksummed.
+	 */
+	if (eb->len >= PAGE_SIZE)
 		set_extent_buffer_uptodate(eb);
+	else
+		SetPageUptodate(eb->pages[0]);
 err:
 	if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
 		clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
@@ -828,7 +896,8 @@ static int btree_csum_one_bio(struct bio *bio)
 	WARN_ON(bio->bi_vcnt <= 0);
 	while (bio_index < bio->bi_vcnt) {
 		root = BTRFS_I(bvec->bv_page->mapping->host)->root;
-		ret = csum_dirty_buffer(root, bvec->bv_page);
+		ret = csum_dirty_buffer(root, bvec->bv_page, bvec->bv_offset,
+					bvec->bv_len);
 		if (ret)
 			break;
 		bio_index++;
@@ -1007,9 +1076,13 @@ static int btree_set_page_dirty(struct page *page)
 	BUG_ON(!PagePrivate(page));
 	eb = (struct extent_buffer *)page->private;
 	BUG_ON(!eb);
-	BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
-	BUG_ON(!atomic_read(&eb->refs));
-	btrfs_assert_tree_locked(eb);
+	/* There doesn't seem to be a method for passing the correct eb
+	 * to this function, so no sanity checks for subpagesize blocksize. */
+	if (eb->len >= PAGE_SIZE) {
+		BUG_ON(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+		BUG_ON(!atomic_read(&eb->refs));
+		btrfs_assert_tree_locked(eb);
+	}
 #endif
 	return __set_page_dirty_nobuffers(page);
 }
@@ -2400,11 +2473,14 @@ int open_ctree(struct super_block *sb,
 		goto fail_sb_buffer;
 	}
 
+#if 0
+	// Hmm. How to deal wth this for subpagesize blocksize?
 	if (sectorsize != PAGE_SIZE) {
 		printk(KERN_WARNING "btrfs: Incompatible sector size(%lu) "
 		       "found on %s\n", (unsigned long)sectorsize, sb->s_id);
 		goto fail_sb_buffer;
 	}
+#endif
 
 	mutex_lock(&fs_info->chunk_mutex);
 	ret = btrfs_read_sys_array(tree_root);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1b319df..c1e052e 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2519,7 +2519,7 @@ static int submit_extent_page(int rw, struct
extent_io_tree *tree,
 	int contig = 0;
 	int this_compressed = bio_flags & EXTENT_BIO_COMPRESSED;
 	int old_compressed = prev_bio_flags & EXTENT_BIO_COMPRESSED;
-	size_t page_size = min_t(size_t, size, PAGE_CACHE_SIZE);
+	size_t bio_size = min_t(size_t, size, PAGE_CACHE_SIZE);
 
 	if (bio_ret && *bio_ret) {
 		bio = *bio_ret;
@@ -2530,8 +2530,8 @@ static int submit_extent_page(int rw, struct
extent_io_tree *tree,
 				sector;
 
 		if (prev_bio_flags != bio_flags || !contig ||
-		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
-		    bio_add_page(bio, page, page_size, offset) < page_size) {
+		    merge_bio(tree, page, offset, bio_size, bio, bio_flags) ||
+		    bio_add_page(bio, page, bio_size, offset) < bio_size) {
 			ret = submit_one_bio(rw, bio, mirror_num,
 					     prev_bio_flags);
 			if (ret < 0)
@@ -2550,7 +2550,7 @@ static int submit_extent_page(int rw, struct
extent_io_tree *tree,
 	if (!bio)
 		return -ENOMEM;
 
-	bio_add_page(bio, page, page_size, offset);
+	bio_add_page(bio, page, bio_size, offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;
 
@@ -3168,14 +3168,28 @@ static void end_bio_extent_buffer_writepage(struct
bio *bio, int err)
 	int uptodate = err == 0;
 	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
 	struct extent_buffer *eb;
+	unsigned int offset;
+	unsigned int bv_len;
+	u64 start;
 	int done;
 
 	do {
 		struct page *page = bvec->bv_page;
+		offset = bvec->bv_offset;
+		bv_len = bvec->bv_len;
+		start = ((u64)page->index << PAGE_CACHE_SHIFT) + offset;
 
 		bvec--;
 		eb = (struct extent_buffer *)page->private;
 		BUG_ON(!eb);
+		if (eb->len < PAGE_SIZE) {
+			while (eb->start != start) {
+				eb = eb->next;
+				BUG_ON(!eb);
+			}
+		}
+
+next_eb:
 		done = atomic_dec_and_test(&eb->io_pages);
 
 		if (!uptodate || test_bit(EXTENT_BUFFER_IOERR, &eb->bflags)) {
@@ -3184,12 +3198,50 @@ static void end_bio_extent_buffer_writepage(struct
bio *bio, int err)
 			SetPageError(page);
 		}
 
-		end_page_writeback(page);
+		if (eb->len >= PAGE_SIZE) {
+			end_page_writeback(page);
 
-		if (!done)
-			continue;
+			if (!done)
+				continue;
 
-		end_extent_buffer_writeback(eb);
+			end_extent_buffer_writeback(eb);
+		} else {
+			/* Sanity checks. */
+			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
+				WARN_ON(1);
+
+			/* Ensure I/O page count is zero. */
+			if (!done)
+				WARN_ON(1);
+
+			/* Clear the extent buffer's writeback flag. */
+			end_extent_buffer_writeback(eb);
+
+			/*
+			 * See if any other extent buffers exists within the
+			 * page.
+			 */
+			bv_len -= eb->len;
+			BUG_ON(bv_len & (eb->len - 1));
+			if (bv_len) {
+				eb = eb->next;
+				goto next_eb;
+			}
+
+			/* Clear the page writeback flag. */
+			eb = (struct extent_buffer *)page->private;
+			BUG_ON(!eb); /* Can this even happen? */
+			do {
+				if (!eb) {
+					end_page_writeback(page);
+					break;
+				}
+				if (test_bit(EXTENT_BUFFER_WRITEBACK,
+					     &eb->bflags))
+					break;
+				eb = eb->next;
+			} while (1);
+		}
 	} while (bvec >= bio->bi_io_vec);
 
 	bio_put(bio);
@@ -3202,7 +3254,8 @@ static int write_one_eb(struct extent_buffer *eb,
 			struct extent_page_data *epd)
 {
 	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
-	u64 offset = eb->start;
+	u64 start = eb->start;
+	unsigned long offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i, num_pages;
 	unsigned long bio_flags = 0;
 	int rw = (epd->sync_io ? WRITE_SYNC : WRITE);
@@ -3219,10 +3272,10 @@ static int write_one_eb(struct extent_buffer *eb,
 
 		clear_page_dirty_for_io(p);
 		set_page_writeback(p);
-		ret = submit_extent_page(rw, eb->tree, p, offset >> 9,
-					 PAGE_CACHE_SIZE, 0, bdev, &epd->bio,
-					 -1, end_bio_extent_buffer_writepage,
-					 0, epd->bio_flags, bio_flags);
+		ret = submit_extent_page(rw, eb->tree, p, start >> 9, eb->len,
+					offset, bdev, &epd->bio, -1,
+					end_bio_extent_buffer_writepage, 0,
+					epd->bio_flags, bio_flags);
 		epd->bio_flags = bio_flags;
 		if (ret) {
 			set_bit(EXTENT_BUFFER_IOERR, &eb->bflags);
@@ -3232,7 +3285,7 @@ static int write_one_eb(struct extent_buffer *eb,
 			ret = -EIO;
 			break;
 		}
-		offset += PAGE_CACHE_SIZE;
+		start += PAGE_CACHE_SIZE;
 		update_nr_written(p, wbc, 1);
 		unlock_page(p);
 	}
@@ -3252,7 +3305,7 @@ int btree_write_cache_pages(struct address_space
*mapping,
 {
 	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
 	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
-	struct extent_buffer *eb, *prev_eb = NULL;
+	struct extent_buffer *eb, *next, *prev_eb = NULL;
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
@@ -3326,17 +3379,41 @@ retry:
 				spin_unlock(&mapping->private_lock);
 				continue;
 			}
+			prev_eb = eb;
+
+next_eb:
+			next = eb->next;
 
 			ret = atomic_inc_not_zero(&eb->refs);
-			spin_unlock(&mapping->private_lock);
-			if (!ret)
-				continue;
+			if (eb->len >= PAGE_SIZE) {
+				spin_unlock(&mapping->private_lock);
+				if (!ret)
+					continue;
+			} else {
+				if (!ret)
+					goto inc_eb;
+				spin_unlock(&mapping->private_lock);
+
+				if (!test_bit(EXTENT_BUFFER_DIRTY,
+					      &eb->bflags)) {
+					spin_lock(&mapping->private_lock);
+					atomic_dec(&eb->refs);
+					ret = 0;
+					goto inc_eb;
+				}
+			}
 
-			prev_eb = eb;
 			ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
 			if (!ret) {
+				if (!(eb->len >= PAGE_SIZE))
+					spin_lock(&mapping->private_lock);
+
 				free_extent_buffer(eb);
-				continue;
+
+				if (eb->len >= PAGE_SIZE)
+					continue;
+				else
+					goto inc_eb;
 			}
 
 			ret = write_one_eb(eb, fs_info, wbc, &epd);
@@ -3345,8 +3422,26 @@ retry:
 				free_extent_buffer(eb);
 				break;
 			}
+
+			if (eb->len >= PAGE_SIZE) {
+				free_extent_buffer(eb);
+				goto written;
+			}
+
+			if (next)
+				spin_lock(&mapping->private_lock);
 			free_extent_buffer(eb);
 
+inc_eb:
+			if (!next) {
+				if (spin_is_locked(&mapping->private_lock))
+					spin_unlock(&mapping->private_lock);
+				goto written;
+			}
+			eb = next;
+			goto next_eb;
+
+written:
 			/*
 			 * the filesystem may choose to bump up nr_to_write.
 			 * We have to make sure to honor the new nr_to_write
@@ -4000,6 +4095,18 @@ static void __free_extent_buffer(struct
extent_buffer *eb)
 	kmem_cache_free(extent_buffer_cache, eb);
 }
 
+/* Helper function to free extent buffers when there are multiple
+ * extent buffers per page. */
+static void __free_extent_buffers(struct extent_buffer *eb)
+{
+	struct extent_buffer *next;
+
+	do {
+		next = eb->next;
+		__free_extent_buffer(eb);
+	} while ((eb = next));
+}
+
 static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree
*tree,
 						   u64 start,
 						   unsigned long len,
@@ -4017,6 +4124,7 @@ static struct extent_buffer
*__alloc_extent_buffer(struct extent_io_tree *tree,
 	eb->len = len;
 	eb->tree = tree;
 	eb->bflags = 0;
+	eb->next = NULL;
 	rwlock_init(&eb->lock);
 	atomic_set(&eb->write_locks, 0);
 	atomic_set(&eb->read_locks, 0);
@@ -4054,6 +4162,62 @@ static struct extent_buffer
*__alloc_extent_buffer(struct extent_io_tree *tree,
 	return eb;
 }
 
+/* Allocates an array of extent buffers for the specified page.
+ * Should be called with the mapping's spin lock set. */
+static struct extent_buffer *__alloc_extent_buffers(struct extent_io_tree
*tree,
+						    struct page *page,
+						    gfp_t mask)
+{
+	u32 blocksize_bits;
+	struct btrfs_inode *inode;
+	struct extent_buffer *eb_head;
+	struct extent_buffer *eb_cur;
+	u64 start;
+	unsigned long len;
+	int i;
+
+	/* Initialize variables. */
+	inode = BTRFS_I(tree->mapping->host);
+	blocksize_bits = inode->vfs_inode.i_sb->s_blocksize_bits;
+
+	/* Calculate extent buffer dimensions. */
+	start = page->index << PAGE_CACHE_SHIFT;
+	len = inode->root->leafsize;
+
+	/* Allocate the head extent buffer. */
+	eb_head = __alloc_extent_buffer(tree, start, len, GFP_NOFS);
+	if (!eb_head) {
+		WARN_ON(1);
+		return NULL;
+	}
+	start += len;
+	eb_head->pages[0] = page;
+	eb_cur = eb_head;
+
+	/* Allocate the other extent buffers. */
+	for (i = 1; i < (PAGE_CACHE_SIZE >> blocksize_bits); i++) {
+		eb_cur->next = __alloc_extent_buffer(tree, start, len,
+						     GFP_NOFS);
+		if (!eb_cur->next) {
+			WARN_ON(1);
+			goto free_ebs;
+		}
+		start += len;
+		eb_cur = eb_cur->next;
+		eb_cur->pages[0] = page;
+	}
+
+	/* Return the extent buffer head. */
+	return eb_head;
+
+free_ebs:
+	/* Free each extent buffer. */
+	// TODO: Implement.
+	pr_crit(KERN_CRIT "HACK: Need to implement this...\n");
+	WARN_ON(1);
+	return NULL;
+}
+
 struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
 {
 	unsigned long i;
@@ -4170,12 +4334,121 @@ static void
btrfs_release_extent_buffer_page(struct extent_buffer *eb,
 }
 
 /*
+ * Frees the page if all extent buffers belonging to the page are not
+ * referernced. The extent buffers themselves must be free afterwards,
too...
+ * ret:	0 if the page did not need to be freed; 1 if the page was freed.
+ */
+static int btrfs_release_extent_buffers_page(struct extent_buffer *eb,
+						struct extent_buffer **eb_head)
+{
+	struct extent_buffer *eb_cur;
+	struct extent_buffer *eb_temp;
+	struct page *page;
+	int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
+	int ret = 0;
+
+	if (extent_buffer_under_io(eb))
+		BUG_ON(1);
+
+	// ...is this even possible?
+	if (!num_extent_pages(eb->start, eb->len)) {
+		WARN_ON(1);
+		return ret;
+	}
+
+	page = extent_buffer_page(eb, 0);
+	if (page && mapped) {
+		spin_lock(&page->mapping->private_lock);
+		/*
+		 * We do this since we'll remove the pages after we've
+		 * removed the eb from the radix tree, so we could race
+		 * and have this page now attached to the new eb.  So
+		 * only clear page_private if it's still connected to
+		 * this eb.
+		 */
+		if (!PagePrivate(page)) {
+			spin_unlock(&page->mapping->private_lock);
+		} else {
+			/* Find the page eb corresponding to our eb. */
+			eb_cur = (struct extent_buffer *)page->private;
+			while (eb_cur->start != eb->start) {
+				eb_cur = eb_cur->next;
+				BUG_ON(!eb_cur);
+			}
+
+			/* See if a new eb has been attached to the page. */
+			if (eb_cur != eb) {
+				spin_unlock(&page->mapping->private_lock);
+				ret = 1;
+				goto page_release;
+			}
+
+			/* See if any other extent_buffer is using the page. */
+			eb_cur = (struct extent_buffer *)page->private;
+			do {
+				/* Check for any other references on the eb. */
+				spin_lock(&eb_cur->refs_lock);
+				if (!atomic_dec_and_test(&eb_cur->refs)) {
+					atomic_inc(&eb_cur->refs);
+					spin_unlock(&eb_cur->refs_lock);
+					eb_temp = eb_cur;
+					eb_cur = (struct extent_buffer *)
+						 page->private;
+					while (eb_cur != eb_temp) {
+						atomic_inc(&eb_cur->refs);
+						eb_cur = eb_cur->next;
+					}
+					spin_unlock(
+						&page->mapping->private_lock);
+					goto page_release;
+				}
+				spin_unlock(&eb_cur->refs_lock);
+			} while ((eb_cur = eb_cur->next) != NULL);
+
+			/* Sanity checks. */
+			eb_cur = (struct extent_buffer *)page->private;
+			do {
+				BUG_ON(extent_buffer_under_io(eb_cur));
+			} while ((eb_cur = eb_cur->next) != NULL);
+			BUG_ON(PageDirty(page));
+			BUG_ON(PageWriteback(page));
+			/*
+			 * We need to make sure we haven't been attached
+			 * to a new eb.
+			 */
+			eb_cur = (struct extent_buffer *)page->private;
+			*eb_head = eb_cur;
+			eb_temp = NULL;
+			ClearPagePrivate(page);
+			set_page_private(page, 0);
+			/* One for the page private. */
+			page_cache_release(page);
+			ret = 1;
+			spin_unlock(&page->mapping->private_lock);
+		}
+	}
+
+page_release:
+	if (page) {
+		/* One for when we alloced the page */
+		page_cache_release(page);
+	}
+	return ret;
+}
+
+/*
  * Helper for releasing the extent buffer.
  */
 static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
 {
-	btrfs_release_extent_buffer_page(eb, 0);
-	__free_extent_buffer(eb);
+	if (eb->len >= PAGE_SIZE) {
+		btrfs_release_extent_buffer_page(eb, 0);
+		__free_extent_buffer(eb);
+	} else {
+		struct extent_buffer *eb_head;
+		if (btrfs_release_extent_buffers_page(eb, &eb_head))
+			__free_extent_buffers(eb_head);
+	}
 }
 
 static void check_buffer_tree_ref(struct extent_buffer *eb)
@@ -4222,16 +4495,153 @@ static void mark_extent_buffer_accessed(struct
extent_buffer *eb)
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 					  u64 start, unsigned long len)
 {
-	unsigned long num_pages = num_extent_pages(start, len);
-	unsigned long i;
-	unsigned long index = start >> PAGE_CACHE_SHIFT;
+	/* Allocate a new extent_buffer depending on blocksize*/
+	if (len < PAGE_CACHE_SIZE)
+		return alloc_extent_buffer_multiple(tree, start, len);
+	return alloc_extent_buffer_single(tree, start, len);
+}
+
+struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree
*tree,
+						   u64 start,
+						   unsigned long len) {
+
+	struct address_space *mapping;
+	u32 blocksize_bits;
+	struct btrfs_inode *btrfs_inode;
+	struct extent_buffer *eb_cur;
+	struct extent_buffer *eb_head;
+	struct extent_buffer *exists;
+	unsigned long index;
+	struct page *page;
+	int ret;
+
+	/* Initialize variables. */
+	btrfs_inode = BTRFS_I(tree->mapping->host);
+	blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
+
+	/* Sanity checks. */
+	WARN_ON(num_extent_pages(start, len) > 1);
+
+	/* See if the extent_buffer already exists in the radix tree. */
+	rcu_read_lock();
+	eb_cur = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
+	if (eb_cur && atomic_inc_not_zero(&eb_cur->refs)) {
+		rcu_read_unlock();
+		mark_extent_buffer_accessed(eb_cur);
+		return eb_cur;
+	}
+	rcu_read_unlock();
+
+	/* Find the page in the mapping. */
+	index = start >> PAGE_CACHE_SHIFT;
+	mapping = tree->mapping;
+	page = find_or_create_page(mapping, index, GFP_NOFS);
+	if (!page) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* Allocate each extent buffer for the page. */
+	eb_head = __alloc_extent_buffers(tree, page, GFP_NOFS);
+	if (!eb_head) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* See if extent buffers have already been allocated for
+	 * this page. */
+	spin_lock(&mapping->private_lock);
+	if (PagePrivate(page)) {
+		/*
+		 * We could have already allocated an eb for this page
+		 * and attached one so lets see if we can get a ref on
+		 * the existing eb, and if we can we know it's good and
+		 * we can just return that one, else we know we can just
+		 * overwrite page->private.
+		 */
+		eb_cur = (struct extent_buffer *)page->private;
+		while (eb_cur->start != start) {
+			eb_cur = eb_cur->next;
+			BUG_ON(!eb_cur);
+		}
+		check_buffer_tree_ref(eb_cur);
+		spin_unlock(&mapping->private_lock);
+		unlock_page(page);
+		mark_extent_buffer_accessed(eb_cur);
+		__free_extent_buffers(eb_head);
+		return eb_cur;
+	}
+
+	/* Bind the extent buffer to the page. */
+	attach_extent_buffer_page(eb_head, page);
+	spin_unlock(&mapping->private_lock);
+	WARN_ON(PageDirty(page));
+	mark_page_accessed(page);
+
+again:
+	/* Set eb_cur to the buffer added. */
+	eb_cur = eb_head;
+	while (start != eb_cur->start) {
+		eb_cur = eb_cur->next;
+		BUG_ON(!eb_cur);
+	}
+
+	/* Preload the radix tree. */
+	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+	if (ret) {
+		WARN_ON(1);
+		return NULL;
+	}
+
+	/* Add the extent buffer to the radix tree. */
+	spin_lock(&tree->buffer_lock);
+	ret = radix_tree_insert(&tree->buffer,
+				eb_cur->start >> blocksize_bits,
+				eb_cur);
+	if (ret == -EEXIST) {
+		exists = radix_tree_lookup(&tree->buffer,
+				eb_cur->start >> blocksize_bits);
+		if (exists->start != start)
+			BUG_ON(1);
+		if (!atomic_inc_not_zero(&exists->refs)) {
+			spin_unlock(&tree->buffer_lock);
+			radix_tree_preload_end();
+			exists = NULL;
+			goto again;
+		}
+		spin_unlock(&tree->buffer_lock);
+		radix_tree_preload_end();
+		mark_extent_buffer_accessed(exists);
+		WARN_ON(!atomic_dec_and_test(&eb_cur->refs));
+		btrfs_release_extent_buffer(eb_cur);
+		return exists;
+	}
+
+	/* Set the extent buffer's tree-reference bits. */
+	check_buffer_tree_ref(eb_cur);
+	spin_unlock(&tree->buffer_lock);
+	radix_tree_preload_end();
+
+	/* Not quite sure what this does. */
+	SetPageChecked(eb_head->pages[0]);
+	unlock_page(eb_head->pages[0]);
+
+	return eb_cur;
+}
+
+struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree
*tree,
+						 u64 start, unsigned long len) {
+	struct address_space *mapping = tree->mapping;
 	struct extent_buffer *eb;
 	struct extent_buffer *exists = NULL;
+	unsigned long i;
+	unsigned long index = start >> PAGE_CACHE_SHIFT;
+	unsigned long num_pages = num_extent_pages(start, len);
 	struct page *p;
-	struct address_space *mapping = tree->mapping;
 	int uptodate = 1;
 	int ret;
 
+	/* See if the extent_buffer already exists */
 	rcu_read_lock();
 	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
@@ -4350,9 +4760,17 @@ struct extent_buffer *find_extent_buffer(struct
extent_io_tree *tree,
 					 u64 start, unsigned long len)
 {
 	struct extent_buffer *eb;
+	struct btrfs_inode *btrfs_inode = BTRFS_I(tree->mapping->host);
+	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
 
 	rcu_read_lock();
-	eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+	// This branch needs to be fixed when the allocation code is merged.
+	// Seriously.
+	if (blocksize_bits >= PAGE_CACHE_SHIFT)
+		eb = radix_tree_lookup(&tree->buffer,
+				       start >> PAGE_CACHE_SHIFT);
+	else
+		eb = radix_tree_lookup(&tree->buffer, start >> blocksize_bits);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
 		rcu_read_unlock();
 		mark_extent_buffer_accessed(eb);
@@ -4371,9 +4789,25 @@ static inline void
btrfs_release_extent_buffer_rcu(struct rcu_head *head)
 	__free_extent_buffer(eb);
 }
 
-/* Expects to have eb->eb_lock already held */
+/*
+ * The RCU head must point to the first extent buffer belonging to a page.
+ */
+static inline void btrfs_release_extent_buffers_rcu(struct rcu_head *head)
+{
+	struct extent_buffer *eb =
+			container_of(head, struct extent_buffer, rcu_head);
+
+	do {
+		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
+	} while ((eb = eb->next));
+}
+
+/* Expects to have eb->refs_lock already held */
 static int release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
 {
+	struct btrfs_inode *btrfs_inode = BTRFS_I(eb->tree->mapping->host);
+	u32 blocksize_bits = btrfs_inode->vfs_inode.i_sb->s_blocksize_bits;
+
 	WARN_ON(atomic_read(&eb->refs) == 0);
 	if (atomic_dec_and_test(&eb->refs)) {
 		if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
@@ -4381,17 +4815,35 @@ static int release_extent_buffer(struct
extent_buffer *eb, gfp_t mask)
 		} else {
 			struct extent_io_tree *tree = eb->tree;
 
+			/* Dumb hack to make releasing the page easier. */
+			if (eb->len < PAGE_SIZE)
+				atomic_inc(&eb->refs);
+
 			spin_unlock(&eb->refs_lock);
 
+			// This also needs to be fixed when allocation code is
+			// merged.
 			spin_lock(&tree->buffer_lock);
-			radix_tree_delete(&tree->buffer,
-					  eb->start >> PAGE_CACHE_SHIFT);
+			if (eb->len >= PAGE_SIZE)
+				radix_tree_delete(&tree->buffer,
+					  eb->start >> blocksize_bits);
+			else
+				radix_tree_delete(&tree->buffer,
+					  eb->start >> blocksize_bits);
 			spin_unlock(&tree->buffer_lock);
 		}
 
 		/* Should be safe to release our pages at this point */
-		btrfs_release_extent_buffer_page(eb, 0);
-		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
+		if (eb->len >= PAGE_SIZE) {
+			btrfs_release_extent_buffer_page(eb, 0);
+			call_rcu(&eb->rcu_head,
+				 btrfs_release_extent_buffer_rcu);
+		} else {
+			struct extent_buffer *eb_head;
+			if (btrfs_release_extent_buffers_page(eb, &eb_head))
+				btrfs_release_extent_buffers_rcu(
+							&eb_head->rcu_head);
+		}
 		return 1;
 	}
 	spin_unlock(&eb->refs_lock);
@@ -4482,6 +4934,11 @@ int set_extent_buffer_dirty(struct extent_buffer
*eb)
 
 	for (i = 0; i < num_pages; i++)
 		set_page_dirty(extent_buffer_page(eb, i));
+	/* Run an additional sanity check here instead of
+	 * in btree_set_page_dirty() since we can't get the eb there for
+	 * subpage blocksize. */
+	if (eb->len < PAGE_SIZE)
+		btrfs_assert_tree_locked(eb);
 	return was_dirty;
 }
 
@@ -4503,11 +4960,14 @@ int clear_extent_buffer_uptodate(struct
extent_buffer *eb)
 	unsigned long num_pages;
 
 	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-	num_pages = num_extent_pages(eb->start, eb->len);
-	for (i = 0; i < num_pages; i++) {
-		page = extent_buffer_page(eb, i);
-		if (page)
-			ClearPageUptodate(page);
+	/* Ignore the page's uptodate flag forsubpage blocksize. */
+	if (eb->len >= PAGE_SIZE) {
+		num_pages = num_extent_pages(eb->start, eb->len);
+		for (i = 0; i < num_pages; i++) {
+			page = extent_buffer_page(eb, i);
+			if (page)
+				ClearPageUptodate(page);
+		}
 	}
 	return 0;
 }
@@ -4518,11 +4978,16 @@ int set_extent_buffer_uptodate(struct extent_buffer
*eb)
 	struct page *page;
 	unsigned long num_pages;
 
+	/* Set extent buffer up-to-date. */
 	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-	num_pages = num_extent_pages(eb->start, eb->len);
-	for (i = 0; i < num_pages; i++) {
-		page = extent_buffer_page(eb, i);
-		SetPageUptodate(page);
+
+	/* Set pages up-to-date. */
+	if (eb->len >= PAGE_CACHE_SIZE) {
+		num_pages = num_extent_pages(eb->start, eb->len);
+		for (i = 0; i < num_pages; i++) {
+			page = extent_buffer_page(eb, i);
+			SetPageUptodate(page);
+		}
 	}
 	return 0;
 }
@@ -4606,7 +5071,7 @@ int read_extent_buffer_pages(struct extent_io_tree
*tree,
 		}
 	}
 	if (all_uptodate) {
-		if (start_i == 0)
+		if (start_i == 0 && eb->len >= PAGE_SIZE)
 			set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 		goto unlock_exit;
 	}
@@ -4693,7 +5158,7 @@ int map_private_extent_buffer(struct extent_buffer
*eb, unsigned long start,
 			       unsigned long *map_start,
 			       unsigned long *map_len)
 {
-	size_t offset = start & (PAGE_CACHE_SIZE - 1);
+	size_t offset;
 	char *kaddr;
 	struct page *p;
 	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
@@ -4709,6 +5174,9 @@ int map_private_extent_buffer(struct extent_buffer
*eb, unsigned long start,
 		*map_start = 0;
 	} else {
 		offset = 0;
+		// I'm pretty sure that this is a) just plain wrong and
+		// b) will never realistically execute; not entirely sure,
+		// though...
 		*map_start = ((u64)i << PAGE_CACHE_SHIFT) - start_offset;
 	}
 
@@ -4722,7 +5190,7 @@ int map_private_extent_buffer(struct extent_buffer
*eb, unsigned long start,
 	p = extent_buffer_page(eb, i);
 	kaddr = page_address(p);
 	*map = kaddr + offset;
-	*map_len = PAGE_CACHE_SIZE - offset;
+	*map_len = (PAGE_CACHE_SIZE - offset) & (eb->len - 1);
 	return 0;
 }
 
@@ -4996,6 +5464,7 @@ void memmove_extent_buffer(struct extent_buffer *dst,
unsigned long dst_offset,
 int try_release_extent_buffer(struct page *page, gfp_t mask)
 {
 	struct extent_buffer *eb;
+	int ret;
 
 	/*
 	 * We need to make sure noboody is attaching this page to an eb right
@@ -5010,30 +5479,61 @@ int try_release_extent_buffer(struct page *page,
gfp_t mask)
 	eb = (struct extent_buffer *)page->private;
 	BUG_ON(!eb);
 
-	/*
-	 * This is a little awful but should be ok, we need to make sure that
-	 * the eb doesn't disappear out from under us while we're looking at
-	 * this page.
-	 */
-	spin_lock(&eb->refs_lock);
-	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
-		spin_unlock(&eb->refs_lock);
+	if (eb->len >= PAGE_SIZE) {
+		/*
+		 * This is a little awful but should be ok, we need to make
+		 * sure that the eb doesn't disappear out from under us while
+		 * we're looking at this page.
+		 */
+		spin_lock(&eb->refs_lock);
+		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
+			spin_unlock(&eb->refs_lock);
+			spin_unlock(&page->mapping->private_lock);
+			return 0;
+		}
 		spin_unlock(&page->mapping->private_lock);
-		return 0;
-	}
-	spin_unlock(&page->mapping->private_lock);
 
-	if ((mask & GFP_NOFS) == GFP_NOFS)
-		mask = GFP_NOFS;
+		if ((mask & GFP_NOFS) == GFP_NOFS)
+			mask = GFP_NOFS;
 
-	/*
-	 * If tree ref isn't set then we know the ref on this eb is a real ref,
-	 * so just return, this page will likely be freed soon anyway.
-	 */
-	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
-		spin_unlock(&eb->refs_lock);
-		return 0;
-	}
+		/*
+		 * If tree ref isn't set then we know the ref on this eb is a
+		 * real ref, so just return, this page will likely be freed
+		 * soon anyway.
+		 */
+		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
+			spin_unlock(&eb->refs_lock);
+			return 0;
+		}
 
-	return release_extent_buffer(eb, mask);
+		return release_extent_buffer(eb, mask);
+	} else {
+		ret = 0;
+		do {
+			spin_lock(&eb->refs_lock);
+			if (atomic_read(&eb->refs) != 1 ||
+					extent_buffer_under_io(eb)) {
+				spin_unlock(&eb->refs_lock);
+				continue;
+			}
+			spin_unlock(&page->mapping->private_lock);
+
+			if ((mask & GFP_NOFS) == GFP_NOFS)
+				mask = GFP_NOFS;
+
+			if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF,
+						&eb->bflags)) {
+				spin_unlock(&eb->refs_lock);
+				spin_lock(&page->mapping->private_lock);
+				continue;
+			}
+
+			/* No idea what to do with the 'ret' here. */
+			ret |= release_extent_buffer(eb, mask);
+
+			spin_lock(&page->mapping->private_lock);
+		} while ((eb = eb->next) != NULL);
+		spin_unlock(&page->mapping->private_lock);
+		return ret;
+	}
 }
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 2eacfab..955ef5e 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -163,6 +163,9 @@ struct extent_buffer {
 	wait_queue_head_t lock_wq;
 	struct page *inline_pages[INLINE_EXTENT_BUFFER_PAGES];
 	struct page **pages;
+
+	/* Acyclic linked list of extent_buffers belonging to a single page. */
+	struct extent_buffer *next;
 };
 
 static inline void extent_set_compress_type(unsigned long *bio_flags,
@@ -270,6 +273,10 @@ void set_page_extent_mapped(struct page *page);
 
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 					  u64 start, unsigned long len);
+struct extent_buffer *alloc_extent_buffer_single(struct extent_io_tree
*tree,
+						 u64 start, unsigned long len);
+struct extent_buffer *alloc_extent_buffer_multiple(struct extent_io_tree
*tree,
+						 u64 start, unsigned long len);
 struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long
len);
 struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer
*src);
 struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3bff4d4..8745289 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1340,7 +1340,7 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
 		}
 
 		ret = btrfs_delalloc_reserve_space(inode,
-					num_pages << PAGE_CACHE_SHIFT);
+					write_bytes);
 		if (ret)
 			break;
 
@@ -1354,7 +1354,7 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
 				    force_page_uptodate);
 		if (ret) {
 			btrfs_delalloc_release_space(inode,
-					num_pages << PAGE_CACHE_SHIFT);
+					write_bytes);
 			break;
 		}
 
@@ -1392,8 +1392,7 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
 				spin_unlock(&BTRFS_I(inode)->lock);
 			}
 			btrfs_delalloc_release_space(inode,
-					(num_pages - dirty_pages) <<
-					PAGE_CACHE_SHIFT);
+						write_bytes - copied);
 		}
 
 		if (copied > 0) {
@@ -1402,7 +1401,7 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
 						NULL);
 			if (ret) {
 				btrfs_delalloc_release_space(inode,
-					dirty_pages << PAGE_CACHE_SHIFT);
+						copied);
 				btrfs_drop_pages(pages, num_pages);
 				break;
 			}
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 59ea2e4..1c0e254 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -960,6 +960,8 @@ int __btrfs_write_out_cache(struct btrfs_root *root,
struct inode *inode,
 
 	if (block_group)
 		start = block_group->key.objectid;
+	else // Hmm I don't recall putting this here.
+		start = (u64)-1;
 
 	while (block_group && (start < block_group->key.objectid +
 			       block_group->key.offset)) {
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3368c10..11ff3dd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2040,22 +2040,38 @@ static int btrfs_writepage_end_io_hook(struct page
*page, u64 start, u64 end,
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_ordered_extent *ordered_extent = NULL;
 	struct btrfs_workers *workers;
+	u64 block_size = 1 << inode->i_blkbits;
+	u64 io_size;
+
+	if (block_size >= PAGE_CACHE_SIZE)
+		io_size = end - start + 1;
+	else
+		io_size = block_size;
 
 	trace_btrfs_writepage_end_io_hook(page, start, end, uptodate);
 
 	ClearPagePrivate2(page);
-	if (!btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
-					    end - start + 1, uptodate))
-		return 0;
-
-	ordered_extent->work.func = finish_ordered_fn;
-	ordered_extent->work.flags = 0;
-
-	if (btrfs_is_free_space_inode(inode))
-		workers = &root->fs_info->endio_freespace_worker;
-	else
-		workers = &root->fs_info->endio_write_workers;
-	btrfs_queue_worker(workers, &ordered_extent->work);
+next_block:
+	if (btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
+					    io_size, uptodate)) {
+		ordered_extent->work.func = finish_ordered_fn;
+		ordered_extent->work.flags = 0;
+
+		if (btrfs_is_free_space_inode(inode))
+			workers = &root->fs_info->endio_freespace_worker;
+		else
+			workers = &root->fs_info->endio_write_workers;
+		btrfs_queue_worker(workers, &ordered_extent->work);
+	}
+
+	// I think that writes are always block-size granularity.
+	if (block_size < PAGE_CACHE_SIZE)
+		BUG_ON(start & (io_size - 1)); // Welp, one way to make sure...
+	start += io_size;
+	if (start < end)
+		goto next_block;
+	// We overshot. I'm pretty sure that this is terrible.
+	BUG_ON(start != (end + 1));
 
 	return 0;
 }
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 657d83c..c0269df 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3937,8 +3937,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(file, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(file, argp);
-	case BTRFS_IOC_DEV_REPLACE:
-		return btrfs_ioctl_dev_replace(root, argp);
+	//case BTRFS_IOC_DEV_REPLACE:
+//		return btrfs_ioctl_dev_replace(root, argp);
 	}
 
 	return -ENOTTY;
-- 
1.7.1

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