From baee8790641eac0c0fcb2524a925aec39d9be6e0 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Tue, 26 Jan 2016 09:35:38 -0500 Subject: [PATCH] Btrfs: check reserved when deciding to background flush We will sometimes start background flushing the various enospc related things (delayed nodes, delalloc, etc) if we are getting close to reserving all of our available space. We don't want to do this however when we are actually using this space as it causes unneeded thrashing. We currently try to do this by checking bytes_used >= thresh, but bytes_used is only part of the equation, we need to use bytes_reserved as well as this represents space that is very likely to become bytes_used in the future. My tracing tool will keep count of the number of times we kick off the async flusher, the following are counts for the entire run of generic/027 No Patch Patch avg: 5385 5009 median: 5500 4916 We skewed lower than the average with my patch and higher than the average with the patch, overall it cuts the flushing from anywhere from 5-10%, which in the case of actual ENOSPC is quite helpful. Thanks, Signed-off-by: Josef Bacik Reviewed-by: Liu Bo Signed-off-by: David Sterba --- fs/btrfs/extent-tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 07f47a5d0d6f..aa31fe97c47a 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -4838,7 +4838,7 @@ static inline int need_do_async_reclaim(struct btrfs_space_info *space_info, u64 thresh = div_factor_fine(space_info->total_bytes, 98); /* If we're just plain full then async reclaim just slows us down. */ - if (space_info->bytes_used >= thresh) + if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh) return 0; return (used >= thresh && !btrfs_fs_closing(fs_info) && -- GitLab