From: Yang Shi <shy828301@gmail.com>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
Dave Chinner <david@fromorbit.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v3 PATCH 05/11] mm: vmscan: use a new flag to indicate shrinker is registered
Date: Tue, 12 Jan 2021 12:58:10 -0800 [thread overview]
Message-ID: <CAHbLzkrOfSSMDhHyemSFWdQ4aSGLytM+9u=s2-BNWsKkLVGgEg@mail.gmail.com> (raw)
In-Reply-To: <ff0d1ed1-e2ae-3e0c-e780-e8d2287cc99b@virtuozzo.com>
On Mon, Jan 11, 2021 at 1:38 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>
> On 11.01.2021 21:17, Yang Shi wrote:
> > On Wed, Jan 6, 2021 at 2:22 AM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> >>
> >> On 06.01.2021 01:58, Yang Shi wrote:
> >>> Currently registered shrinker is indicated by non-NULL shrinker->nr_deferred.
> >>> This approach is fine with nr_deferred at the shrinker level, but the following
> >>> patches will move MEMCG_AWARE shrinkers' nr_deferred to memcg level, so their
> >>> shrinker->nr_deferred would always be NULL. This would prevent the shrinkers
> >>> from unregistering correctly.
> >>>
> >>> Signed-off-by: Yang Shi <shy828301@gmail.com>
> >>> ---
> >>> include/linux/shrinker.h | 7 ++++---
> >>> mm/vmscan.c | 13 +++++++++----
> >>> 2 files changed, 13 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> >>> index 0f80123650e2..1eac79ce57d4 100644
> >>> --- a/include/linux/shrinker.h
> >>> +++ b/include/linux/shrinker.h
> >>> @@ -79,13 +79,14 @@ struct shrinker {
> >>> #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
> >>>
> >>> /* Flags */
> >>> -#define SHRINKER_NUMA_AWARE (1 << 0)
> >>> -#define SHRINKER_MEMCG_AWARE (1 << 1)
> >>> +#define SHRINKER_REGISTERED (1 << 0)
> >>> +#define SHRINKER_NUMA_AWARE (1 << 1)
> >>> +#define SHRINKER_MEMCG_AWARE (1 << 2)
> >>> /*
> >>> * It just makes sense when the shrinker is also MEMCG_AWARE for now,
> >>> * non-MEMCG_AWARE shrinker should not have this flag set.
> >>> */
> >>> -#define SHRINKER_NONSLAB (1 << 2)
> >>> +#define SHRINKER_NONSLAB (1 << 3)
> >>>
> >>> extern int prealloc_shrinker(struct shrinker *shrinker);
> >>> extern void register_shrinker_prepared(struct shrinker *shrinker);
> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> index 8da765a85569..9761c7c27412 100644
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -494,6 +494,7 @@ void register_shrinker_prepared(struct shrinker *shrinker)
> >>> if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>> idr_replace(&shrinker_idr, shrinker, shrinker->id);
> >>> #endif
> >>> + shrinker->flags |= SHRINKER_REGISTERED;
> >>
> >> In case of we introduce this new flag, we should kill old flag SHRINKER_REGISTERING,
> >> which are not needed anymore (we should you the new flag instead of that).
> >
> > The only think that I'm confused with is the check in
> > shrink_slab_memcg, it does:
> >
> > shrinker = idr_find(&shrinker_idr, i);
> > if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
> >
> > When allocating idr, the shrinker is associated with
> > SHRINKER_REGISTERING. But, shrink_slab_memcg does acquire read
> > shrinker_rwsem, and idr_alloc is called with holding write
> > shrinker_rwsem, so I'm supposed shrink_slab_memcg should never see
> > shrinker is registering.
>
> After prealloc_shrinker() shrinker is visible for shrink_slab_memcg().
> This is the moment shrink_slab_memcg() sees SHRINKER_REGISTERED.
Yes, this exactly is what I'm supposed.
>
> > If so it seems easy to remove
> > SHRINKER_REGISTERING.
> >
> > We just need change that check to:
> > !shrinker || !(shrinker->flags & SHRINKER_REGISTERED)
> >
> >>> up_write(&shrinker_rwsem);
> >>> }
> >>>
> >>> @@ -513,13 +514,17 @@ EXPORT_SYMBOL(register_shrinker);
> >>> */
> >>> void unregister_shrinker(struct shrinker *shrinker)
> >>> {
> >>> - if (!shrinker->nr_deferred)
> >>> - return;
> >>> - if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>> - unregister_memcg_shrinker(shrinker);
> >>> down_write(&shrinker_rwsem);
> >>
> >> I do not think there are some users which registration may race with unregistration.
> >> So, I think we should check SHRINKER_REGISTERED unlocked similar to we used to check
> >> shrinker->nr_deferred unlocked.
> >
> > Yes, I agree.
> >
> >>
> >>> + if (!(shrinker->flags & SHRINKER_REGISTERED)) {
> >>> + up_write(&shrinker_rwsem);
> >>> + return;
> >>> + }
> >>> list_del(&shrinker->list);
> >>> + shrinker->flags &= ~SHRINKER_REGISTERED;
> >>> up_write(&shrinker_rwsem);
> >>> +
> >>> + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> >>> + unregister_memcg_shrinker(shrinker);
> >>> kfree(shrinker->nr_deferred);
> >>> shrinker->nr_deferred = NULL;
> >>> }
> >>>
> >>
> >>
>
>
next prev parent reply other threads:[~2021-01-12 20:58 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 22:58 [RFC v3 PATCH 0/11] Make shrinker's nr_deferred memcg aware Yang Shi
2021-01-05 22:58 ` [v3 PATCH 01/11] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-01-05 22:58 ` [v3 PATCH 02/11] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-01-07 0:13 ` Roman Gushchin
2021-01-07 17:29 ` Yang Shi
2021-01-11 19:00 ` Yang Shi
2021-01-11 19:37 ` Roman Gushchin
2021-01-11 19:43 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2021-01-06 9:54 ` Kirill Tkhai
2021-01-11 17:08 ` Yang Shi
2021-01-11 17:33 ` Kirill Tkhai
2021-01-11 18:57 ` Yang Shi
2021-01-11 21:33 ` Kirill Tkhai
2021-01-12 21:23 ` Yang Shi
2021-01-13 18:16 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 04/11] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-01-06 10:15 ` Kirill Tkhai
2021-01-11 17:44 ` Yang Shi
2021-01-13 23:48 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 05/11] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-01-06 10:21 ` Kirill Tkhai
2021-01-11 18:17 ` Yang Shi
2021-01-11 21:37 ` Kirill Tkhai
2021-01-12 20:58 ` Yang Shi [this message]
2021-01-05 22:58 ` [v3 PATCH 06/11] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-01-06 11:38 ` Kirill Tkhai
2021-01-11 18:19 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 07/11] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-01-06 11:06 ` Kirill Tkhai
2021-01-11 18:24 ` Yang Shi
2021-01-13 23:30 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-01-07 0:17 ` Roman Gushchin
2021-01-07 17:34 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-01-06 11:15 ` Kirill Tkhai
2021-01-11 18:40 ` Yang Shi
2021-01-11 21:57 ` Kirill Tkhai
2021-01-05 22:58 ` [v3 PATCH 10/11] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-01-06 11:34 ` Kirill Tkhai
2021-01-11 18:43 ` Yang Shi
2021-01-05 22:58 ` [v3 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
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