From: Qu Wenruo Date: Wed, 17 Sep 2014 11:53:35 +0800 Subject: [PATCH] btrfs: Fix and enhance merge_extent_mapping() to insert best fitted extent map (cherry picked from commit e6c4efd87ab04e5ead363f24e6ac35ed3506d401) The following commit enhanced the merge_extent_mapping() to reduce fragment in extent map tree, but it can't handle case which existing lies before map_start: 51f39 btrfs: Use right extent length when inserting overlap extent map. [BUG] When existing extent map's start is before map_start, the em->len will be minus, which will corrupt the extent map and fail to insert the new extent map. This will happen when someone get a large extent map, but when it is going to insert it into extent map tree, some one has already commit some write and split the huge extent into small parts. [REPRODUCER] It is very easy to tiger using filebench with randomrw personality. It is about 100% to reproduce when using 8G preallocated file in 60s randonrw test. [FIX] This patch can now handle any existing extent position. Since it does not directly use existing->start, now it will find the previous and next extent around map_start. So the old existing->start < map_start bug will never happen again. [ENHANCE] This patch will insert the best fitted extent map into extent map tree, other than the oldest [map_start, map_start + sectorsize) or the relatively newer but not perfect [map_start, existing->start). The patch will first search existing extent that does not intersects with the desired map range [map_start, map_start + len). The existing extent will be either before or behind map_start, and based on the existing extent, we can find out the previous and next extent around map_start. So the best fitted extent would be [prev->end, next->start). For prev or next is not found, em->start would be prev->end and em->end wold be next->start. With this patch, the fragment in extent map tree should be reduced much more than the 51f39 commit and reduce an unneeded extent map tree search. Reported-by: Tsutomu Itoh Signed-off-by: Qu Wenruo Signed-off-by: Chris Mason --- fs/btrfs/inode.c | 79 ++++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 57 insertions(+), 22 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 016c403bfe7e..8039021353ab 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -6191,21 +6191,60 @@ out_fail_inode: goto out_fail; } +/* Find next extent map of a given extent map, caller needs to ensure locks */ +static struct extent_map *next_extent_map(struct extent_map *em) +{ + struct rb_node *next; + + next = rb_next(&em->rb_node); + if (!next) + return NULL; + return container_of(next, struct extent_map, rb_node); +} + +static struct extent_map *prev_extent_map(struct extent_map *em) +{ + struct rb_node *prev; + + prev = rb_prev(&em->rb_node); + if (!prev) + return NULL; + return container_of(prev, struct extent_map, rb_node); +} + /* helper for btfs_get_extent. Given an existing extent in the tree, + * the existing extent is the nearest extent to map_start, * and an extent that you want to insert, deal with overlap and insert - * the new extent into the tree. + * the best fitted new extent into the tree. */ static int merge_extent_mapping(struct extent_map_tree *em_tree, struct extent_map *existing, struct extent_map *em, u64 map_start) { + struct extent_map *prev; + struct extent_map *next; + u64 start; + u64 end; u64 start_diff; BUG_ON(map_start < em->start || map_start >= extent_map_end(em)); - start_diff = map_start - em->start; - em->start = map_start; - em->len = existing->start - em->start; + + if (existing->start > map_start) { + next = existing; + prev = prev_extent_map(next); + } else { + prev = existing; + next = next_extent_map(prev); + } + + start = prev ? extent_map_end(prev) : em->start; + start = max_t(u64, start, em->start); + end = next ? next->start : extent_map_end(em); + end = min_t(u64, end, extent_map_end(em)); + start_diff = start - em->start; + em->start = start; + em->len = end - start; if (em->block_start < EXTENT_MAP_LAST_BYTE && !test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) { em->block_start += start_diff; @@ -6482,25 +6521,21 @@ insert: ret = 0; - existing = lookup_extent_mapping(em_tree, start, len); - if (existing && (existing->start > start || - existing->start + existing->len <= start)) { + existing = search_extent_mapping(em_tree, start, len); + /* + * existing will always be non-NULL, since there must be + * extent causing the -EEXIST. + */ + if (start >= extent_map_end(existing) || + start + len <= existing->start) { + /* + * The existing extent map is the one nearest to + * the [start, start + len) range which overlaps + */ + err = merge_extent_mapping(em_tree, existing, + em, start); free_extent_map(existing); - existing = NULL; - } - if (!existing) { - existing = lookup_extent_mapping(em_tree, em->start, - em->len); - if (existing) { - err = merge_extent_mapping(em_tree, existing, - em, start); - free_extent_map(existing); - if (err) { - free_extent_map(em); - em = NULL; - } - } else { - err = -EIO; + if (err) { free_extent_map(em); em = NULL; } -- 1.9.3