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Date:   Tue, 15 Dec 2020 17:45:40 +0100
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Kirill Tkhai <tkhai@ya.ru>
Cc:     Yang Shi <shy828301@gmail.com>, "guro@fb.com" <guro@fb.com>,
        "ktkhai@virtuozzo.com" <ktkhai@virtuozzo.com>,
        "shakeelb@google.com" <shakeelb@google.com>,
        "david@fromorbit.com" <david@fromorbit.com>,
        "mhocko@suse.com" <mhocko@suse.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [v2 PATCH 3/9] mm: vmscan: guarantee shrinker_slab_memcg() sees
 valid shrinker_maps for online memcg
Message-ID: <20201215164540.GB385334@cmpxchg.org>
References: <20201214223722.232537-1-shy828301@gmail.com>
 <20201214223722.232537-4-shy828301@gmail.com>
 <20201215123802.GA379720@cmpxchg.org>
 <1874151608036985@mail.yandex.ru>
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On Tue, Dec 15, 2020 at 03:58:06PM +0300, Kirill Tkhai wrote:
> 15.12.2020, 15:40, "Johannes Weiner" <hannes@cmpxchg.org>:
> > On Mon, Dec 14, 2020 at 02:37:16PM -0800, Yang Shi wrote:
> >> ?The 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 we will see
> >> ?memcg->nodeinfo[nid]->shrinker_maps != NULL. This may occur because of processor reordering
> >> ?on !x86.
> >>
> >> ?This seems like the below case:
> >>
> >> ????????????CPU A CPU B
> >> ?store shrinker_map load CSS_ONLINE
> >> ?store CSS_ONLINE load shrinker_map
> >>
> >> ?So the memory ordering could be guaranteed by smp_wmb()/smp_rmb() pair.
> >>
> >> ?The memory barriers pair will guarantee the ordering between shrinker_deferred and CSS_ONLINE
> >> ?for the following patches as well.
> >>
> >> ?Signed-off-by: Yang Shi <shy828301@gmail.com>
> >
> > As per previous feedback, please move the misplaced shrinker
> > allocation callback from .css_online to .css_alloc. This will get you
> > the necessary ordering guarantees from the cgroup core code.
> 
> 
> Can you read my emails from ktkhai@virtuozzo.com? I've already answered
> on this question here: https://lkml.org/lkml/2020/12/10/726
> 
> Check your spam folder, and add my address to allow-list if so.

It was indeed in my spam folder. Disregard what I wrote above.