Josef Bacik
2013-Feb-06 18:58 UTC
[PATCH] Btrfs: rework the overcommit logic to be based on the total size
People have been complaining about random ENOSPC errors that will clear up after a umount or just a given amount of time. Chris was able to reproduce this with stress.sh and lots of processes and so was I. Basically the overcommit stuff would really let us get out of hand, in my tests I saw up to 30 gigs of outstanding reservations with only 2 gigs total of metadata space. This usually worked out fine but with so much outstanding reservation the flushing stuff short circuits to make sure we don''t hang forever flushing when we really need ENOSPC. Plus we allocate chunks in order to alleviate the pressure, but this doesn''t actually help us since we only use the non-allocated area in our over commit logic. So instead of basing overcommit on the amount of non-allocated space, instead just do it based on how much total space we have, and then limit it to the non-allocated space in case we are short on space to spill over into. This allows us to have the same performance as well as no longer giving random ENOSPC. Thanks, Signed-off-by: Josef Bacik <jbacik@fusionio.com> --- fs/btrfs/extent-tree.c | 15 ++++++++++++--- 1 files changed, 12 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 11ffa16..981130b 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -3677,6 +3677,7 @@ static int can_overcommit(struct btrfs_root *root, u64 rsv_size = 0; u64 avail; u64 used; + u64 to_add; used = space_info->bytes_used + space_info->bytes_reserved + space_info->bytes_pinned + space_info->bytes_readonly; @@ -3710,17 +3711,25 @@ static int can_overcommit(struct btrfs_root *root, BTRFS_BLOCK_GROUP_RAID10)) avail >>= 1; + to_add = space_info->total_bytes; + /* * If we aren''t flushing all things, let us overcommit up to * 1/2th of the space. If we can flush, don''t let us overcommit * too much, let it overcommit up to 1/8 of the space. */ if (flush == BTRFS_RESERVE_FLUSH_ALL) - avail >>= 3; + to_add >>= 3; else - avail >>= 1; + to_add >>= 1; + + /* + * Limit the overcommit to the amount of free space we could possibly + * allocate for chunks. + */ + to_add = min(avail, to_add); - if (used + bytes < space_info->total_bytes + avail) + if (used + bytes < space_info->total_bytes + to_add) return 1; return 0; } -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html