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Message-ID: <bab60fe4-964c-43a6-ecce-4cbd4981d875@ya.ru>
Date: Thu, 1 Jun 2023 03:57:10 +0300
From: Kirill Tkhai <tkhai@...ru>
To: Qi Zheng <qi.zheng@...ux.dev>, paulmck@...nel.org
Cc: RCU <rcu@...r.kernel.org>, Yujie Liu <yujie.liu@...el.com>,
oe-lkp@...ts.linux.dev, lkp@...el.com,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Christian König <christian.koenig@....com>,
David Hildenbrand <david@...hat.com>,
Davidlohr Bueso <dave@...olabs.net>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Muchun Song <muchun.song@...ux.dev>,
Shakeel Butt <shakeelb@...gle.com>,
Yang Shi <shy828301@...il.com>, linux-mm@...ck.org,
ying.huang@...el.com, feng.tang@...el.com, fengwei.yin@...el.com
Subject: Re: [linus:master] [mm] f95bdb700b: stress-ng.ramfs.ops_per_sec
-88.8% regression
Hi,
On 30.05.2023 06:07, Qi Zheng wrote:
> Hi,
>
> On 2023/5/29 20:51, Paul E. McKenney wrote:
>> On Mon, May 29, 2023 at 10:39:21AM +0800, Qi Zheng wrote:
>
> [...]
>
>>>
>>> Thanks for such a detailed explanation.
>>>
>>> Now I think we can continue to try to complete the idea[1] from
>>> Kirill Tkhai. The patch moves heavy synchronize_srcu() to delayed
>>> work, so it doesn't affect on user-visible unregistration speed.
>>>
>>> [1]. https://lore.kernel.org/lkml/153365636747.19074.12610817307548583381.stgit@localhost.localdomain/
>>
>> A blast from the past! ;-)
>>
>> But yes, moving the long-latency synchronize_srcu() off the user-visible
>> critical code path can be even better.
>
> Yeah, I applied these patches ([PATCH RFC 04/10]~[PATCH RFC 10/10],
> with few conflicts), the ops/s does get back to the previous levels.
>
> I'll continue updating this patchset after doing more testing.
You may also fix the issue using the below generic solution.
In addition to this we need patch, which calls unregister_shrinker_delayed_initiate()
instead of unregister_shrinker() in deactivate_locked_super(), and calls
unregister_shrinker_delayed_finalize() from destroy_super_work(). Compilation tested only.
---
include/linux/shrinker.h | 2 ++
mm/vmscan.c | 38 ++++++++++++++++++++++++++++++--------
2 files changed, 32 insertions(+), 8 deletions(-)
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 224293b2dd06..4ba2986716d3 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -4,6 +4,7 @@
#include <linux/atomic.h>
#include <linux/types.h>
+#include <linux/rwsem.h>
/*
* This struct is used to pass information from page reclaim to the shrinkers.
@@ -83,6 +84,7 @@ struct shrinker {
#endif
/* objs pending delete, per node */
atomic_long_t *nr_deferred;
+ struct rw_semaphore rwsem;
};
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index eeca83e28c9b..19fc129771ce 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -706,6 +706,7 @@ static int __prealloc_shrinker(struct shrinker *shrinker)
if (!shrinker->nr_deferred)
return -ENOMEM;
+ init_rwsem(&shrinker->rwsem);
return 0;
}
@@ -757,7 +758,9 @@ void register_shrinker_prepared(struct shrinker *shrinker)
{
mutex_lock(&shrinker_mutex);
list_add_tail_rcu(&shrinker->list, &shrinker_list);
+ down_write(&shrinker->rwsem);
shrinker->flags |= SHRINKER_REGISTERED;
+ up_write(&shrinker->rwsem);
shrinker_debugfs_add(shrinker);
mutex_unlock(&shrinker_mutex);
}
@@ -802,7 +805,7 @@ EXPORT_SYMBOL(register_shrinker);
/*
* Remove one
*/
-void unregister_shrinker(struct shrinker *shrinker)
+void unregister_shrinker_delayed_initiate(struct shrinker *shrinker)
{
struct dentry *debugfs_entry;
int debugfs_id;
@@ -812,20 +815,33 @@ void unregister_shrinker(struct shrinker *shrinker)
mutex_lock(&shrinker_mutex);
list_del_rcu(&shrinker->list);
+ down_write(&shrinker->rwsem);
shrinker->flags &= ~SHRINKER_REGISTERED;
+ up_write(&shrinker->rwsem);
if (shrinker->flags & SHRINKER_MEMCG_AWARE)
unregister_memcg_shrinker(shrinker);
debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
mutex_unlock(&shrinker_mutex);
+ shrinker_debugfs_remove(debugfs_entry, debugfs_id); // This is moved in your patch
+}
+EXPORT_SYMBOL(unregister_shrinker_delayed_initiate);
+
+void unregister_shrinker_delayed_finalize(struct shrinker *shrinker)
+{
atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
- shrinker_debugfs_remove(debugfs_entry, debugfs_id);
-
kfree(shrinker->nr_deferred);
shrinker->nr_deferred = NULL;
}
+EXPORT_SYMBOL(unregister_shrinker_delayed_finalize);
+
+void unregister_shrinker(struct shrinker *shrinker)
+{
+ unregister_shrinker_delayed_initiate(shrinker);
+ unregister_shrinker_delayed_finalize(shrinker);
+}
EXPORT_SYMBOL(unregister_shrinker);
/**
@@ -856,9 +872,14 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
: SHRINK_BATCH;
long scanned = 0, next_deferred;
+ down_read(&shrinker->rwsem);
+ if (!(shrinker->flags & SHRINKER_REGISTERED))
+ goto unlock;
freeable = shrinker->count_objects(shrinker, shrinkctl);
- if (freeable == 0 || freeable == SHRINK_EMPTY)
- return freeable;
+ if (freeable == 0 || freeable == SHRINK_EMPTY) {
+ freed = freeable;
+ goto unlock;
+ }
/*
* copy the current shrinker scan count into a local variable
@@ -935,6 +956,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
* manner that handles concurrent updates.
*/
new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
+unlock:
+ up_read(&shrinker->rwsem);
trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
return freed;
@@ -968,9 +991,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
struct shrinker *shrinker;
shrinker = idr_find(&shrinker_idr, i);
- if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
- if (!shrinker)
- clear_bit(i, info->map);
+ if (unlikely(!shrinker)) {
+ clear_bit(i, info->map);
continue;
}
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