FAILED: patch "[PATCH] fs: fix missed removal of super_fs_objects_eligible()" failed to apply to 7.2-stable tree

The patch below does not apply to the 7.2-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
git checkout FETCH_HEAD
git cherry-pick -x 641aade99f06df0037e52b5c81645461b7132947
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092250-stool-feed-1f18@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 641aade99f06df0037e52b5c81645461b7132947 Mon Sep 17 00:00:00 2001
From: Qi Zheng <[email protected]>
Date: Mon, 17 Aug 2026 17:03:25 +0800
Subject: [PATCH] fs: fix missed removal of super_fs_objects_eligible()

Commit 0ef8faff490be ("fs: push nr_cached_objects memcg gating into individual filesystems") was meant to drop the blanket memcg gate in fs/super.c and let each ->nr_cached_objects() implementation decide for itself whether it is meaningful in per-memcg reclaim. However, when that patch was applied the removal of super_fs_objects_eligible() and its two call sites in super_cache_scan() / super_cache_count() was lost, so the helper is still gating every ->nr_cached_objects() hook and 0ef8faff490be is effectively a no-op.

Consequences of the leftover gate:

- XFS's inode-reclaim hook, which is intentionally driven from per-memcg contexts to free memcg-charged slab, is still short-circuited in fs/super.c exactly the regression from commit 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink") that 0ef8faff490be was written to undo. Memcg-charged XFS inode slab therefore keeps piling up under per-memcg pressure until global reclaim kicks in.

- Any future ->nr_cached_objects()/->free_cached_objects() that grows memcg awareness is likewise blocked before it can run, so filesystems cannot opt in to per-memcg reclaim on their own defeating the whole point of pushing the gating decision down into the callbacks.

Drop the leftover helper and its call sites so the intent of 0ef8faff490be actually takes effect.

index 05e443173038..3ecce24328f6 100644
@@ -171,19 +171,6 @@ static void super_wake(struct super_block *sb, unsigned int flag)
 	wake_up_var(&sb->s_flags);
 }
 
-/*
- * The s_op->nr_cached_objects hooks (used for example by btrfs and xfs)
- * operate on filesystem-global state and ignore sc->memcg. Driving them
- * from per-memcg shrink_slab_memcg() invocations only burns CPU walking
- * per-cpu counters and queueing duplicate work: the actual reclaim happens on
- * the global path (kswapd or root direct reclaim) regardless. Restrict them
- * to that path.
- */
-static inline bool super_fs_objects_eligible(struct shrink_control *sc)
-{
-	return !sc->memcg || mem_cgroup_is_root(sc->memcg);
-}
-
 /*
  * One thing we have to be careful of with a per-sb shrinker is that we don't
  * drop the last active reference to the superblock from within the shrinker.

@@ -213,7 +200,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!super_trylock_shared(sb))
 		return SHRINK_STOP;
 
-	if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc))
+	if (sb->s_op->nr_cached_objects)
 		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);

@@ -274,8 +261,7 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 		return 0;
 	smp_rmb();
 
-	if (sb->s_op && sb->s_op->nr_cached_objects &&
-	    super_fs_objects_eligible(sc))
+	if (sb->s_op && sb->s_op->nr_cached_objects)
 		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);

From: Usama Arif <[email protected]>

[ Upstream commit 0baad6f9b9970c6e3f1d33dbfd17d1a77702771d ]

The super_block shrinker is registered with SHRINKER_MEMCG_AWARE because its dentry and inode LRUs are memcg-aware (via list_lru). But the optional ->nr_cached_objects() hooks that the shrinker also drives are not memcg-aware:
btrfs extent maps and xfs inode reclaim operate on filesystem-global state, and shmem's unused-huge shrinker walks a per-superblock shrinklist. None of them filter by sc->memcg.

The mismatch shows up under memcg-heavy slab reclaim. shrink_slab_memcg() calls do_shrink_slab() once per (memcg, NUMA node) pair for every memcg whose bit is set in the per-superblock shrinker bitmap, which on a busy host means hundreds of calls per reclaim pass. Each scan queues the same global shrinker work item that's already kicked from the root path.

Because btrfs/xfs global count is typically non-zero on any in-use filesystem, the returned total stays positive even if a memcg's own dentry/inode LRUs are empty. shrink_slab_memcg() therefore never clears the SB shrinker bit in the memcg bitmap, so subsequent reclaim passes from the same memcg re-enter super_cache_count() and pay for the global counter walk again.

Restrict ->nr_cached_objects() to the global shrink path (sc->memcg NULL or root). The memcg-aware dentry/inode LRUs keep being counted and scanned per memcg as before; only the global fs-specific hooks are skipped. The root/global shrink path still drives those hooks; only their invocation from non-root memcg slab reclaim is removed.

Stable-dep-of: 641aade99f06 ("fs: fix missed removal of super_fs_objects_eligible()")

---
 fs/super.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

index 1159a73856db6..feac9ba5abe81 100644
@@ -24,6 +24,7 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
+#include <linux/memcontrol.h>
 #include <linux/mount.h>
 #include <linux/security.h>
 #include <linux/writeback.h>		/* for the emergency remount stuff */

@@ -169,6 +170,19 @@ static void super_wake(struct super_block *sb, unsigned int flag)
 	wake_up_var(&sb->s_flags);
 }
 
+/*
+ * The s_op->nr_cached_objects hooks (used for example by btrfs and xfs)
+ * operate on filesystem-global state and ignore sc->memcg. Driving them
+ * from per-memcg shrink_slab_memcg() invocations only burns CPU walking
+ * per-cpu counters and queueing duplicate work: the actual reclaim happens on
+ * the global path (kswapd or root direct reclaim) regardless. Restrict them
+ * to that path.
+ */
+static inline bool super_fs_objects_eligible(struct shrink_control *sc)
+{
+	return !sc->memcg || mem_cgroup_is_root(sc->memcg);
+}
+
 /*
  * One thing we have to be careful of with a per-sb shrinker is that we don't
  * drop the last active reference to the superblock from within the shrinker.

@@ -198,7 +212,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!super_trylock_shared(sb))
 		return SHRINK_STOP;
 
-	if (sb->s_op->nr_cached_objects)
+	if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc))
 		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);

@@ -259,7 +273,8 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 		return 0;
 	smp_rmb();
 
-	if (sb->s_op && sb->s_op->nr_cached_objects)
+	if (sb->s_op && sb->s_op->nr_cached_objects &&
+	    super_fs_objects_eligible(sc))
 		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);

2.53.0

From: Qi Zheng <[email protected]>

[ Upstream commit 641aade99f06df0037e52b5c81645461b7132947 ]

Commit 0ef8faff490be ("fs: push nr_cached_objects memcg gating into individual filesystems") was meant to drop the blanket memcg gate in fs/super.c and let each ->nr_cached_objects() implementation decide for itself whether it is meaningful in per-memcg reclaim. However, when that patch was applied the removal of super_fs_objects_eligible() and its two call sites in super_cache_scan() / super_cache_count() was lost, so the helper is still gating every ->nr_cached_objects() hook and 0ef8faff490be is effectively a no-op.

Consequences of the leftover gate:

- XFS's inode-reclaim hook, which is intentionally driven from per-memcg contexts to free memcg-charged slab, is still short-circuited in fs/super.c exactly the regression from commit 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink") that 0ef8faff490be was written to undo. Memcg-charged XFS inode slab therefore keeps piling up under per-memcg pressure until global reclaim kicks in.

- Any future ->nr_cached_objects()/->free_cached_objects() that grows memcg awareness is likewise blocked before it can run, so filesystems cannot opt in to per-memcg reclaim on their own defeating the whole point of pushing the gating decision down into the callbacks.

Drop the leftover helper and its call sites so the intent of 0ef8faff490be actually takes effect.

---
 fs/super.c | 18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

index feac9ba5abe81..a257b154f7f7f 100644
@@ -170,19 +170,6 @@ static void super_wake(struct super_block *sb, unsigned int flag)
 	wake_up_var(&sb->s_flags);
 }
 
-/*
- * The s_op->nr_cached_objects hooks (used for example by btrfs and xfs)
- * operate on filesystem-global state and ignore sc->memcg. Driving them
- * from per-memcg shrink_slab_memcg() invocations only burns CPU walking
- * per-cpu counters and queueing duplicate work: the actual reclaim happens on
- * the global path (kswapd or root direct reclaim) regardless. Restrict them
- * to that path.
- */
-static inline bool super_fs_objects_eligible(struct shrink_control *sc)
-{
-	return !sc->memcg || mem_cgroup_is_root(sc->memcg);
-}
-
 /*
  * One thing we have to be careful of with a per-sb shrinker is that we don't
  * drop the last active reference to the superblock from within the shrinker.

@@ -212,7 +199,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	if (!super_trylock_shared(sb))
 		return SHRINK_STOP;
 
-	if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc))
+	if (sb->s_op->nr_cached_objects)
 		fs_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);

@@ -273,8 +260,7 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 		return 0;
 	smp_rmb();
 
-	if (sb->s_op && sb->s_op->nr_cached_objects &&
-	    super_fs_objects_eligible(sc))
+	if (sb->s_op && sb->s_op->nr_cached_objects)
 		total_objects = sb->s_op->nr_cached_objects(sb, sc);
 
 	total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);

2.53.0