From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Yang Shi <shy828301@gmail.com>,
guro@fb.com, shakeelb@google.com, david@fromorbit.com,
hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker
Date: Thu, 3 Dec 2020 14:40:25 +0300 [thread overview]
Message-ID: <49464720-675d-5144-043c-eba6852a9c06@virtuozzo.com> (raw)
In-Reply-To: <20201202182725.265020-7-shy828301@gmail.com>
On 02.12.2020 21:27, Yang Shi wrote:
> Use per memcg's nr_deferred for memcg aware shrinkers. The shrinker's nr_deferred
> will be used in the following cases:
> 1. Non memcg aware shrinkers
> 2. !CONFIG_MEMCG
> 3. memcg is disabled by boot parameter
>
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
> mm/vmscan.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 82 insertions(+), 6 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index cba0bc8d4661..d569fdcaba79 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -203,6 +203,12 @@ static DECLARE_RWSEM(shrinker_rwsem);
> static DEFINE_IDR(shrinker_idr);
> static int shrinker_nr_max;
>
> +static inline bool is_deferred_memcg_aware(struct shrinker *shrinker)
> +{
> + return (shrinker->flags & SHRINKER_MEMCG_AWARE) &&
> + !mem_cgroup_disabled();
> +}
> +
> static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> {
> int id, ret = -ENOMEM;
> @@ -271,7 +277,58 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> #endif
> return false;
> }
> +
> +static inline long count_nr_deferred(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + bool per_memcg_deferred = is_deferred_memcg_aware(shrinker) && sc->memcg;
> + struct memcg_shrinker_deferred *deferred;
> + struct mem_cgroup *memcg = sc->memcg;
> + int nid = sc->nid;
> + int id = shrinker->id;
> + long nr;
> +
> + if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> + nid = 0;
> +
> + if (per_memcg_deferred) {
> + deferred = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_deferred,
> + true);
My comment is about both 5/9 and 6/9 patches.
shrink_slab_memcg() races with mem_cgroup_css_online(). A visibility of CSS_ONLINE flag
in shrink_slab_memcg()->mem_cgroup_online() does not guarantee that you will see
memcg->nodeinfo[nid]->shrinker_deferred != NULL in count_nr_deferred(). This may occur
because of processor reordering on !x86 (there is no a common lock or memory barriers).
Regarding to shrinker_map this is not a problem due to map check in shrink_slab_memcg().
The map can't be NULL there.
Regarding to shrinker_deferred you should prove either this is not a problem too,
or to add proper synchronization (maybe, based on barriers) or to add some similar check
(maybe, in shrink_slab_memcg() too).
Kirill
next prev parent reply other threads:[~2020-12-03 11:40 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 18:27 [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Yang Shi
2020-12-02 18:27 ` [PATCH 1/9] mm: vmscan: simplify nr_deferred update code Yang Shi
2020-12-03 2:56 ` Roman Gushchin
2020-12-02 18:27 ` [PATCH 2/9] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2020-12-03 3:13 ` Xiaqing (A)
2020-12-11 19:20 ` Yang Shi
2020-12-02 18:27 ` [PATCH 3/9] mm: memcontrol: rename memcg_shrinker_map_mutex to memcg_shrinker_mutex Yang Shi
2020-12-02 18:27 ` [PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2020-12-03 3:01 ` Roman Gushchin
2020-12-03 4:59 ` Yang Shi
2020-12-03 20:08 ` Roman Gushchin
2020-12-03 22:25 ` Yang Shi
2020-12-04 18:52 ` Johannes Weiner
2020-12-04 21:24 ` Yang Shi
2020-12-02 18:27 ` [PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred Yang Shi
2020-12-03 3:06 ` Roman Gushchin
2020-12-03 4:54 ` Yang Shi
2020-12-03 18:03 ` Yang Shi
2020-12-03 20:07 ` Roman Gushchin
2020-12-03 22:49 ` Yang Shi
2020-12-03 23:30 ` Roman Gushchin
2020-12-04 0:22 ` Yang Shi
2020-12-10 15:33 ` Johannes Weiner
2020-12-10 19:12 ` Yang Shi
2020-12-11 17:52 ` Yang Shi
2020-12-10 21:59 ` Yang Shi
2020-12-02 18:27 ` [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2020-12-03 3:08 ` Roman Gushchin
2020-12-03 5:01 ` Yang Shi
2020-12-03 11:40 ` Kirill Tkhai [this message]
2020-12-08 17:13 ` Yang Shi
2020-12-09 15:41 ` Kirill Tkhai
2020-12-09 17:32 ` Yang Shi
2020-12-10 15:13 ` Johannes Weiner
2020-12-10 15:17 ` Kirill Tkhai
2020-12-15 16:44 ` Johannes Weiner
2020-12-02 18:27 ` [PATCH 7/9] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2020-12-02 18:27 ` [PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2020-12-02 18:27 ` [PATCH 9/9] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
2020-12-03 2:52 ` [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Roman Gushchin
2020-12-03 17:52 ` Yang Shi
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