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authorQi Zheng <zhengqi.arch@bytedance.com>2023-06-09 10:15:15 +0200
committerAndrew Morton <akpm@linux-foundation.org>2023-06-19 22:19:34 +0200
commit1a554ecc971406e291cea867112f7f2e377e810e (patch)
tree328f6ee3a972f4d27cf3f6dc593d43fdf98eeaaf /mm/shrinker_debug.c
parentRevert "mm: vmscan: hold write lock to reparent shrinker nr_deferred" (diff)
downloadlinux-1a554ecc971406e291cea867112f7f2e377e810e.tar.xz
linux-1a554ecc971406e291cea867112f7f2e377e810e.zip
Revert "mm: shrinkers: make count and scan in shrinker debugfs lockless"
This reverts commit 20cd1892fcc3efc10a7ac327cc3790494bec46b5. 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. 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_srcu related changes first. [1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/ [2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/ Link: https://lkml.kernel.org/r/20230609081518.3039120-5-qi.zheng@linux.dev Reported-by: kernel test robot <yujie.liu@intel.com> Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@intel.com Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Kirill Tkhai <tkhai@ya.ru> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/shrinker_debug.c')
-rw-r--r--mm/shrinker_debug.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 2be15b8a6d0b..3ab53fad8876 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -5,12 +5,10 @@
#include <linux/seq_file.h>
#include <linux/shrinker.h>
#include <linux/memcontrol.h>
-#include <linux/srcu.h>
/* defined in vmscan.c */
extern struct rw_semaphore shrinker_rwsem;
extern struct list_head shrinker_list;
-extern struct srcu_struct shrinker_srcu;
static DEFINE_IDA(shrinker_debugfs_ida);
static struct dentry *shrinker_debugfs_root;
@@ -51,13 +49,18 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
struct mem_cgroup *memcg;
unsigned long total;
bool memcg_aware;
- int ret = 0, nid, srcu_idx;
+ int ret, nid;
count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL);
if (!count_per_node)
return -ENOMEM;
- srcu_idx = srcu_read_lock(&shrinker_srcu);
+ ret = down_read_killable(&shrinker_rwsem);
+ if (ret) {
+ kfree(count_per_node);
+ return ret;
+ }
+ rcu_read_lock();
memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
@@ -88,7 +91,8 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v)
}
} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
- srcu_read_unlock(&shrinker_srcu, srcu_idx);
+ rcu_read_unlock();
+ up_read(&shrinker_rwsem);
kfree(count_per_node);
return ret;
@@ -111,8 +115,9 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
.gfp_mask = GFP_KERNEL,
};
struct mem_cgroup *memcg = NULL;
- int nid, srcu_idx;
+ int nid;
char kbuf[72];
+ ssize_t ret;
read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
if (copy_from_user(kbuf, buf, read_len))
@@ -141,7 +146,11 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
return -EINVAL;
}
- srcu_idx = srcu_read_lock(&shrinker_srcu);
+ ret = down_read_killable(&shrinker_rwsem);
+ if (ret) {
+ mem_cgroup_put(memcg);
+ return ret;
+ }
sc.nid = nid;
sc.memcg = memcg;
@@ -150,7 +159,7 @@ static ssize_t shrinker_debugfs_scan_write(struct file *file,
shrinker->scan_objects(shrinker, &sc);
- srcu_read_unlock(&shrinker_srcu, srcu_idx);
+ up_read(&shrinker_rwsem);
mem_cgroup_put(memcg);
return size;