The patch titled
Subject: Revert "mm: shrinkers: convert shrinker_rwsem to mutex"
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: Revert "mm: shrinkers: convert shrinker_rwsem to mutex"
Date: Fri, 9 Jun 2023 08:15:12 +0000
Patch series "revert shrinker_srcu related changes".
This patch (of 7):
This reverts commit cf2e309ebca7bb0916771839f9b580b06c778530.
Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec
test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make
global slab shrink lockless"). The root cause is that SRCU has to be
careful to not frequently check for SRCU read-side critical section exits.
Therefore, even if no one is currently in the SRCU read-side critical
section, synchronize_srcu() cannot return quickly. That's why
unregister_shrinker() has become slower.
After discussion, we will try to use the refcount+RCU method [2] proposed
by Dave Chinner to continue to re-implement the lockless slab shrink. So
revert the shrinker_mutex back to shrinker_rwsem first.
[1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@xxxxxxxxx/
[2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@xxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20230609081518.3039120-1-qi.zheng@xxxxxxxxx
Link: https://lkml.kernel.org/r/20230609081518.3039120-2-qi.zheng@xxxxxxxxx
Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@xxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Kirill Tkhai <tkhai@xxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yujie Liu <yujie.liu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-cache-metadata.c | 2 -
drivers/md/dm-thin-metadata.c | 2 -
fs/super.c | 2 -
mm/shrinker_debug.c | 14 ++++++------
mm/vmscan.c | 34 +++++++++++++++----------------
5 files changed, 27 insertions(+), 27 deletions(-)
--- a/drivers/md/dm-cache-metadata.c~revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex
+++ a/drivers/md/dm-cache-metadata.c
@@ -1828,7 +1828,7 @@ int dm_cache_metadata_abort(struct dm_ca
* Replacement block manager (new_bm) is created and old_bm destroyed outside of
* cmd root_lock to avoid ABBA deadlock that would result (due to life-cycle of
* shrinker associated with the block manager's bufio client vs cmd root_lock).
- * - must take shrinker_mutex without holding cmd->root_lock
+ * - must take shrinker_rwsem without holding cmd->root_lock
*/
new_bm = dm_block_manager_create(cmd->bdev, DM_CACHE_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
CACHE_MAX_CONCURRENT_LOCKS);
--- a/drivers/md/dm-thin-metadata.c~revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex
+++ a/drivers/md/dm-thin-metadata.c
@@ -1887,7 +1887,7 @@ int dm_pool_abort_metadata(struct dm_poo
* Replacement block manager (new_bm) is created and old_bm destroyed outside of
* pmd root_lock to avoid ABBA deadlock that would result (due to life-cycle of
* shrinker associated with the block manager's bufio client vs pmd root_lock).
- * - must take shrinker_mutex without holding pmd->root_lock
+ * - must take shrinker_rwsem without holding pmd->root_lock
*/
new_bm = dm_block_manager_create(pmd->bdev, THIN_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
THIN_MAX_CONCURRENT_LOCKS);
--- a/fs/super.c~revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex
+++ a/fs/super.c
@@ -54,7 +54,7 @@ static char *sb_writers_name[SB_FREEZE_L
* 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.
* If that happens we could trigger unregistering the shrinker from within the
- * shrinker path and that leads to deadlock on the shrinker_mutex. Hence we
+ * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
* take a passive reference to the superblock to avoid this from occurring.
*/
static unsigned long super_cache_scan(struct shrinker *shrink,
--- a/mm/shrinker_debug.c~revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex
+++ a/mm/shrinker_debug.c
@@ -8,7 +8,7 @@
#include <linux/srcu.h>
/* defined in vmscan.c */
-extern struct mutex shrinker_mutex;
+extern struct rw_semaphore shrinker_rwsem;
extern struct list_head shrinker_list;
extern struct srcu_struct shrinker_srcu;
@@ -168,7 +168,7 @@ int shrinker_debugfs_add(struct shrinker
char buf[128];
int id;
- lockdep_assert_held(&shrinker_mutex);
+ lockdep_assert_held(&shrinker_rwsem);
/* debugfs isn't initialized yet, add debugfs entries later. */
if (!shrinker_debugfs_root)
@@ -211,7 +211,7 @@ int shrinker_debugfs_rename(struct shrin
if (!new)
return -ENOMEM;
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
old = shrinker->name;
shrinker->name = new;
@@ -229,7 +229,7 @@ int shrinker_debugfs_rename(struct shrin
shrinker->debugfs_entry = entry;
}
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
kfree_const(old);
@@ -242,7 +242,7 @@ struct dentry *shrinker_debugfs_detach(s
{
struct dentry *entry = shrinker->debugfs_entry;
- lockdep_assert_held(&shrinker_mutex);
+ lockdep_assert_held(&shrinker_rwsem);
kfree_const(shrinker->name);
shrinker->name = NULL;
@@ -271,14 +271,14 @@ static int __init shrinker_debugfs_init(
shrinker_debugfs_root = dentry;
/* Create debugfs entries for shrinkers registered at boot */
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
list_for_each_entry(shrinker, &shrinker_list, list)
if (!shrinker->debugfs_entry) {
ret = shrinker_debugfs_add(shrinker);
if (ret)
break;
}
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
return ret;
}
--- a/mm/vmscan.c~revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex
+++ a/mm/vmscan.c
@@ -35,7 +35,7 @@
#include <linux/cpuset.h>
#include <linux/compaction.h>
#include <linux/notifier.h>
-#include <linux/mutex.h>
+#include <linux/rwsem.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
@@ -190,7 +190,7 @@ struct scan_control {
int vm_swappiness = 60;
LIST_HEAD(shrinker_list);
-DEFINE_MUTEX(shrinker_mutex);
+DECLARE_RWSEM(shrinker_rwsem);
DEFINE_SRCU(shrinker_srcu);
static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0);
@@ -213,7 +213,7 @@ static struct shrinker_info *shrinker_in
{
return srcu_dereference_check(memcg->nodeinfo[nid]->shrinker_info,
&shrinker_srcu,
- lockdep_is_held(&shrinker_mutex));
+ lockdep_is_held(&shrinker_rwsem));
}
static struct shrinker_info *shrinker_info_srcu(struct mem_cgroup *memcg,
@@ -292,7 +292,7 @@ int alloc_shrinker_info(struct mem_cgrou
int nid, size, ret = 0;
int map_size, defer_size = 0;
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
map_size = shrinker_map_size(shrinker_nr_max);
defer_size = shrinker_defer_size(shrinker_nr_max);
size = map_size + defer_size;
@@ -308,7 +308,7 @@ int alloc_shrinker_info(struct mem_cgrou
info->map_nr_max = shrinker_nr_max;
rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
}
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
return ret;
}
@@ -324,7 +324,7 @@ static int expand_shrinker_info(int new_
if (!root_mem_cgroup)
goto out;
- lockdep_assert_held(&shrinker_mutex);
+ lockdep_assert_held(&shrinker_rwsem);
map_size = shrinker_map_size(new_nr_max);
defer_size = shrinker_defer_size(new_nr_max);
@@ -374,7 +374,7 @@ static int prealloc_memcg_shrinker(struc
if (mem_cgroup_disabled())
return -ENOSYS;
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
if (id < 0)
goto unlock;
@@ -388,7 +388,7 @@ static int prealloc_memcg_shrinker(struc
shrinker->id = id;
ret = 0;
unlock:
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
return ret;
}
@@ -398,7 +398,7 @@ static void unregister_memcg_shrinker(st
BUG_ON(id < 0);
- lockdep_assert_held(&shrinker_mutex);
+ lockdep_assert_held(&shrinker_rwsem);
idr_remove(&shrinker_idr, id);
}
@@ -433,7 +433,7 @@ void reparent_shrinker_deferred(struct m
parent = root_mem_cgroup;
/* Prevent from concurrent shrinker_info expand */
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
for_each_node(nid) {
child_info = shrinker_info_protected(memcg, nid);
parent_info = shrinker_info_protected(parent, nid);
@@ -442,7 +442,7 @@ void reparent_shrinker_deferred(struct m
atomic_long_add(nr, &parent_info->nr_deferred[i]);
}
}
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
}
static bool cgroup_reclaim(struct scan_control *sc)
@@ -743,9 +743,9 @@ void free_prealloced_shrinker(struct shr
shrinker->name = NULL;
#endif
if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
unregister_memcg_shrinker(shrinker);
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
return;
}
@@ -755,11 +755,11 @@ void free_prealloced_shrinker(struct shr
void register_shrinker_prepared(struct shrinker *shrinker)
{
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
list_add_tail_rcu(&shrinker->list, &shrinker_list);
shrinker->flags |= SHRINKER_REGISTERED;
shrinker_debugfs_add(shrinker);
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
}
static int __register_shrinker(struct shrinker *shrinker)
@@ -810,13 +810,13 @@ void unregister_shrinker(struct shrinker
if (!(shrinker->flags & SHRINKER_REGISTERED))
return;
- mutex_lock(&shrinker_mutex);
+ down_write(&shrinker_rwsem);
list_del_rcu(&shrinker->list);
shrinker->flags &= ~SHRINKER_REGISTERED;
if (shrinker->flags & SHRINKER_MEMCG_AWARE)
unregister_memcg_shrinker(shrinker);
debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
- mutex_unlock(&shrinker_mutex);
+ up_write(&shrinker_rwsem);
atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
revert-mm-shrinkers-convert-shrinker_rwsem-to-mutex.patch
revert-mm-vmscan-remove-shrinker_rwsem-from-synchronize_shrinkers.patch
revert-mm-vmscan-hold-write-lock-to-reparent-shrinker-nr_deferred.patch
revert-mm-shrinkers-make-count-and-scan-in-shrinker-debugfs-lockless.patch
revert-mm-vmscan-add-shrinker_srcu_generation.patch
revert-mm-vmscan-make-memcg-slab-shrink-lockless.patch
revert-mm-vmscan-make-global-slab-shrink-lockless.patch
mm-vmscan-move-shrinker_debugfs_remove-before-synchronize_srcu.patch
