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[5/5] btrfs: re-enable the extent map shrinker

Message ID 2ddc45133bcee20c64699abf10cc24bf2737b606.1727174151.git.fdmanana@suse.com (mailing list archive)
State New
Headers show
Series btrfs: make extent map shrinker more efficient and re-enable it | expand

Commit Message

Filipe Manana Sept. 24, 2024, 10:45 a.m. UTC 
From: Filipe Manana <fdmanana@suse.com>

Now that the extent map shrinker can only be run by a single task and runs
asynchronously as a work queue job, enable it as it can no longer cause
stalls on tasks allocating memory and entering the extent map shrinker
through the fs shrinker (implemented by btrfs_free_cached_objects()).

This is crucial to prevent exhaustion of memory due to unbounded extent
map creation, primarily with direct IO but also for buffered IO on files
with holes. This problem, for the direct IO case, was first reported in
the Link tag below. That report was added to a Link tag of the first patch
that introduced the extent map shrinker, commit 956a17d9d050 ("btrfs: add
a shrinker for extent maps"), however the Link tag disappeared somehow
from the committed patch (but was included in the submitted patch to the
mailing list), so adding it below for future reference.

Link: https://lore.kernel.org/linux-btrfs/13f94633dcf04d29aaf1f0a43d42c55e@amazon.com/
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/super.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)
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Patch

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e9e209dd8e05..7e20b5e8386c 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2401,13 +2401,7 @@  static long btrfs_nr_cached_objects(struct super_block *sb, struct shrink_contro
 
 	trace_btrfs_extent_map_shrinker_count(fs_info, nr);
 
-	/*
-	 * Only report the real number for EXPERIMENTAL builds, as there are
-	 * reports of serious performance degradation caused by too frequent shrinks.
-	 */
-	if (IS_ENABLED(CONFIG_BTRFS_EXPERIMENTAL))
-		return nr;
-	return 0;
+	return nr;
 }
 
 static long btrfs_free_cached_objects(struct super_block *sb, struct shrink_control *sc)