From: Josef Bacik <josef@toxicpanda.com>
Date: Wed, 28 Apr 2021 13:38:46 -0400
Subject: btrfs: don't include the global rsv size in the preemptive used amount
Git-commit: 30acce4eb032251be4767ee393a7e6e9748259d6
Patch-mainline: v5.14-rc1
References: bsc#1202528

When deciding if we should preemptively flush space, we will add in the
amount of space used by all block rsvs.  However this also includes the
global block rsv, which isn't flushable so shouldn't be accounted for in
this calculation.  If we decide to use ->bytes_may_use in our used
calculation we need to subtract the global rsv size from this amount so
it most closely matches the flushable space.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/space-info.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index fedf3440145a..0e88a1482624 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -871,7 +871,7 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
 		used += fs_info->delayed_refs_rsv.reserved +
 			fs_info->delayed_block_rsv.reserved;
 	else
-		used += space_info->bytes_may_use;
+		used += space_info->bytes_may_use - global_rsv_size;
 
 	return (used >= thresh && !btrfs_fs_closing(fs_info) &&
 		!test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));