From: Josef Bacik <josef@toxicpanda.com>
Date: Fri, 9 Oct 2020 09:28:25 -0400
Subject: btrfs: rework btrfs_calc_reclaim_metadata_size
Git-commit: 9f42d37748264d65ca611b60c22b9c003030b0b3
Patch-mainline: v5.12-rc1
References: bsc#1202528

Currently btrfs_calc_reclaim_metadata_size does two things, it returns
the space currently required for flushing by the tickets, and if there
are no tickets it calculates a value for the preemptive flushing.

However for the normal ticketed flushing we really only care about the
space required for tickets.  We will accidentally come in and flush one
time, but as soon as we see there are no tickets we bail out of our
flushing.

Fix this by making btrfs_calc_reclaim_metadata_size really only tell us
what is required for flushing if we have people waiting on space.  Then
move the preemptive flushing logic into need_preemptive_reclaim().  We
ignore btrfs_calc_reclaim_metadata_size() in need_preemptive_reclaim()
because if we are in this path then we made our reservation and there
are not pending tickets currently, so we do not need to check it, simply
do the fuzzy logic to check if we're getting low on space.

Reviewed-by: Nikolay Borisov <nborisov@suse.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 |   44 ++++++++++++++++++++------------------------
 1 file changed, 20 insertions(+), 24 deletions(-)

--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -643,7 +643,6 @@ btrfs_calc_reclaim_metadata_size(struct
 {
 	u64 used;
 	u64 avail;
-	u64 expected;
 	u64 to_reclaim = space_info->reclaim_size;
 
 	lockdep_assert_held(&space_info->lock);
@@ -661,28 +660,6 @@ btrfs_calc_reclaim_metadata_size(struct
 	if (space_info->total_bytes + avail < used)
 		to_reclaim += used - (space_info->total_bytes + avail);
 
-	if (to_reclaim)
-		return to_reclaim;
-
-	to_reclaim = min_t(u64, num_online_cpus() * SZ_1M, SZ_16M);
-	if (btrfs_can_overcommit(fs_info, space_info, to_reclaim,
-			   BTRFS_RESERVE_FLUSH_ALL))
-		return 0;
-
-	used = space_info->bytes_used + space_info->bytes_reserved +
-	       space_info->bytes_pinned + space_info->bytes_readonly +
-	       space_info->bytes_may_use;
-	if (btrfs_can_overcommit(fs_info, space_info, SZ_1M, BTRFS_RESERVE_FLUSH_ALL))
-		expected = div_factor_fine(space_info->total_bytes, 95);
-	else
-		expected = div_factor_fine(space_info->total_bytes, 90);
-
-	if (used > expected)
-		to_reclaim = used - expected;
-	else
-		to_reclaim = 0;
-	to_reclaim = min(to_reclaim, space_info->bytes_may_use +
-				     space_info->bytes_reserved);
 	return to_reclaim;
 }
 
@@ -691,6 +668,7 @@ static bool need_preemptive_reclaim(stru
 				    u64 used)
 {
 	u64 thresh = div_factor_fine(space_info->total_bytes, 98);
+	u64 to_reclaim, expected;
 
 	/* If we're just plain full then async reclaim just slows us down. */
 	if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh)
@@ -703,7 +681,25 @@ static bool need_preemptive_reclaim(stru
 	if (space_info->reclaim_size)
 		return false;
 
-	if (!btrfs_calc_reclaim_metadata_size(fs_info, space_info))
+	to_reclaim = min_t(u64, num_online_cpus() * SZ_1M, SZ_16M);
+	if (btrfs_can_overcommit(fs_info, space_info, to_reclaim,
+				 BTRFS_RESERVE_FLUSH_ALL))
+		return false;
+
+	used = btrfs_space_info_used(space_info, true);
+	if (btrfs_can_overcommit(fs_info, space_info, SZ_1M,
+				 BTRFS_RESERVE_FLUSH_ALL))
+		expected = div_factor_fine(space_info->total_bytes, 95);
+	else
+		expected = div_factor_fine(space_info->total_bytes, 90);
+
+	if (used > expected)
+		to_reclaim = used - expected;
+	else
+		to_reclaim = 0;
+	to_reclaim = min(to_reclaim, space_info->bytes_may_use +
+				     space_info->bytes_reserved);
+	if (!to_reclaim)
 		return false;
 
 	return (used >= thresh && !btrfs_fs_closing(fs_info) &&