From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>, 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>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: BUG: Bad page state in process - page dumped because: page still charged to cgroup
Date: Thu, 2 Jul 2020 18:35:31 +0200 [thread overview]
Message-ID: <57270a15-a792-5175-757b-c4bde6da3694@suse.cz> (raw)
In-Reply-To: <20200702162202.GI18446@dhcp22.suse.cz>
On 7/2/20 6:22 PM, Michal Hocko wrote:
> 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>
Fixes: ? or let Andrew squash it to some patch of your series (it's in mmotm I
think)?
Acked-by: Vlastimil Babka <vbabka@suse.cz>
But see below:
>> ---
>> 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?
Yes, and drop the if(). It will just do nothing and return if already enabled.
Maybe slightly less efficient, but this is not a fast path anyway, and it feels
weird to modify the static key in a branch controlled by the static key itself
(CC peterz in case he wants to add something).
>> /*
>> * 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
>
next prev parent reply other threads:[~2020-07-02 16:35 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
2020-07-02 16:35 ` Vlastimil Babka [this message]
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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