From: Michal Hocko <mhocko@kernel.org>
To: Roman Gushchin <guro@fb.com>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
Shakeel Butt <shakeelb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
open list <linux-kernel@vger.kernel.org>,
lkft-triage@lists.linaro.org, Chris Down <chris@chrisdown.name>
Subject: Re: BUG: Bad page state in process - page dumped because: page still charged to cgroup
Date: Thu, 2 Jul 2020 18:22:02 +0200 [thread overview]
Message-ID: <20200702162202.GI18446@dhcp22.suse.cz> (raw)
In-Reply-To: <20200701184552.GA61684@carbon.DHCP.thefacebook.com>
On Wed 01-07-20 11:45:52, Roman Gushchin wrote:
[...]
> >From c97afecd32c0db5e024be9ba72f43d22974f5bcd Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <guro@fb.com>
> Date: Wed, 1 Jul 2020 11:05:32 -0700
> Subject: [PATCH] mm: kmem: make memcg_kmem_enabled() irreversible
>
> Historically the kernel memory accounting was an opt-in feature, which
> could be enabled for individual cgroups. But now it's not true, and
> it's on by default both on cgroup v1 and cgroup v2. And as long as a
> user has at least one non-root memory cgroup, the kernel memory
> accounting is on. So in most setups it's either always on (if memory
> cgroups are in use and kmem accounting is not disabled), either always
> off (otherwise).
>
> memcg_kmem_enabled() is used in many places to guard the kernel memory
> accounting code. If memcg_kmem_enabled() can reverse from returning
> true to returning false (as now), we can't rely on it on release paths
> and have to check if it was on before.
>
> If we'll make memcg_kmem_enabled() irreversible (always returning true
> after returning it for the first time), it'll make the general logic
> more simple and robust. It also will allow to guard some checks which
> otherwise would stay unguarded.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> ---
> mm/memcontrol.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 50ae77f3985e..2d018a51c941 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3582,7 +3582,8 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
> objcg->memcg = memcg;
> rcu_assign_pointer(memcg->objcg, objcg);
>
> - static_branch_inc(&memcg_kmem_enabled_key);
> + if (!memcg_kmem_enabled())
> + static_branch_inc(&memcg_kmem_enabled_key);
Wouldn't be static_branch_enable() more readable?
> /*
> * A memory cgroup is considered kmem-online as soon as it gets
> * kmemcg_id. Setting the id after enabling static branching will
> @@ -3643,9 +3644,6 @@ static void memcg_free_kmem(struct mem_cgroup *memcg)
> /* css_alloc() failed, offlining didn't happen */
> if (unlikely(memcg->kmem_state == KMEM_ONLINE))
> memcg_offline_kmem(memcg);
> -
> - if (memcg->kmem_state == KMEM_ALLOCATED)
> - static_branch_dec(&memcg_kmem_enabled_key);
> }
> #else
> static int memcg_online_kmem(struct mem_cgroup *memcg)
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-07-02 16:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-01 8:18 BUG: Bad page state in process - page dumped because: page still charged to cgroup Naresh Kamboju
2020-07-01 8:29 ` Michal Hocko
2020-07-01 12:31 ` Naresh Kamboju
2020-07-01 18:45 ` Roman Gushchin
2020-07-02 6:19 ` Michal Hocko
2020-07-02 6:52 ` Naresh Kamboju
2020-07-02 15:49 ` Roman Gushchin
2020-07-02 15:55 ` Naresh Kamboju
2020-07-02 15:59 ` Roman Gushchin
2020-07-02 16:02 ` Shakeel Butt
2020-07-02 16:22 ` Michal Hocko [this message]
2020-07-02 16:35 ` Vlastimil Babka
2020-07-02 17:07 ` Roman Gushchin
2020-07-02 17:10 ` Michal Hocko
2020-07-02 16:37 ` Roman Gushchin
2020-07-02 17:13 ` Michal Hocko
2020-07-02 17:19 ` Roman Gushchin
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