From: Haifeng Xu <haifeng.xu@shopee.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mhocko@suse.com, hannes@cmpxchg.org, roman.gushchin@linux.dev,
shakeelb@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, vmpressure: remove redundant check in vmpressure()
Date: Thu, 20 Apr 2023 10:25:25 +0800 [thread overview]
Message-ID: <9fb84281-19ce-8a39-b87b-fcadf9d265d1@shopee.com> (raw)
In-Reply-To: <20230419130311.587b7273eca2512c07b32bd0@linux-foundation.org>
On 2023/4/20 04:03, Andrew Morton wrote:
> On Wed, 19 Apr 2023 09:20:07 +0000 Haifeng Xu <haifeng.xu@shopee.com> wrote:
>
>> There are three places, vmpressure_prio(), shrink_node_memcgs() and
>> shrink_node(), which invoke vmpressure(). But only shrink_node_memcgs()
>> sets tree to false and the memcg used in it is not NULL, so we don't
>> check it again in vmpressure().
>>
>> ...
>>
>> --- a/mm/vmpressure.c
>> +++ b/mm/vmpressure.c
>> @@ -284,7 +284,7 @@ void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
>> enum vmpressure_levels level;
>>
>> /* For now, no users for root-level efficiency */
>> - if (!memcg || mem_cgroup_is_root(memcg))
>> + if (mem_cgroup_is_root(memcg))
>> return;
>>
>> spin_lock(&vmpr->sr_lock);
>
> try_to_free_pages()->
> do_try_to_free_pages()->
> vmpressure_prio()->
> vmpressure()->
> crash
>
> what am I missing here?
>
>
vmpressure_prio() set tree to true, so the crash won't happen.
> It does appear that vmpressure() could be simplified with
>
> if (!memcg)
> memcg = root_mem_cgroup;
>
> so the test you identified goes away and the memcg_to_vmpressure() call
> becomes simpler. But that's such a small change it doesn't seem worth
> the effort.
memcg_to_vmpressure() has taken this case that the memcg is NULL into account and
we do not need to change it.
The test I identified is in the branch that the tree is set to false. In this branch,
memcg can never be NULL because only shrink_node_memcgs() will step into it.
prev parent reply other threads:[~2023-04-20 2:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-19 9:20 Haifeng Xu
2023-04-19 20:03 ` Andrew Morton
2023-04-20 2:25 ` Haifeng Xu [this message]
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