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Btrfs: fix extent entry threshold calculation 

There is a slight problem with the extent entry threshold calculation for the
free space cache.  We only adjust the threshold down as we add bitmaps, but
never actually adjust the threshold up as we add bitmaps.  This means we could
fragment the free space so badly that we end up using all bitmaps to describe
the free space, use all the free space which would result in the bitmaps being
freed, but then go to add free space again as we delete things and immediately
add bitmaps since the extent threshold would still be 0.  Now as we free
bitmaps the extent threshold will be ratcheted up to allow more extent entries
to be added.

Signed-off-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Josef Bacik 2009-09-11 16:11:20 -04:00 committed by Chris Mason
parent f61408b81c
commit 25891f796d
1 changed files with 22 additions and 15 deletions
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37
fs/btrfs/free-space-cache.c
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@ -259,7 +259,9 @@ static int link_free_space(struct btrfs_block_group_cache *block_group,
static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
{
u64 max_bytes, possible_bytes;
u64 max_bytes;
u64 bitmap_bytes;
u64 extent_bytes;
/*
* The goal is to keep the total amount of memory used per 1gb of space
@ -269,22 +271,27 @@ static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
max_bytes = MAX_CACHE_BYTES_PER_GIG *
(div64_u64(block_group->key.offset, 1024 * 1024 * 1024));
possible_bytes = (block_group->total_bitmaps * PAGE_CACHE_SIZE) +
(sizeof(struct btrfs_free_space) *
block_group->extents_thresh);
/*
* we want to account for 1 more bitmap than what we have so we can make
* sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
* we add more bitmaps.
*/
bitmap_bytes = (block_group->total_bitmaps + 1) * PAGE_CACHE_SIZE;
if (possible_bytes > max_bytes) {
int extent_bytes = max_bytes -
(block_group->total_bitmaps * PAGE_CACHE_SIZE);
if (extent_bytes <= 0) {
block_group->extents_thresh = 0;
return;
}
block_group->extents_thresh = extent_bytes /
(sizeof(struct btrfs_free_space));
if (bitmap_bytes >= max_bytes) {
block_group->extents_thresh = 0;
return;
}
/*
* we want the extent entry threshold to always be at most 1/2 the maxw
* bytes we can have, or whatever is less than that.
*/
extent_bytes = max_bytes - bitmap_bytes;
extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));
block_group->extents_thresh =
div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
}
static void bitmap_clear_bits(struct btrfs_block_group_cache *block_group,