Message-ID: <4b2b0132-eb6f-d0a9-e6bb-6b23d3cbcd48@shopee.com>
Date:   Tue, 7 Mar 2023 11:20:10 +0800
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Subject: Re: [PATCH] mm: remove redundant check in handle_mm_fault
To:     Matthew Wilcox <willy@infradead.org>
Cc:     David Hildenbrand <david@redhat.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20230306024959.131468-1-haifeng.xu@shopee.com>
 <df3997ed-a844-597b-fbb1-154caad78543@redhat.com>
 <354360d5-dce6-a11c-ee61-d41e615bfa05@shopee.com>
 <ZAamFX/hq6Y/iNJb@casper.infradead.org>
From:   Haifeng Xu <haifeng.xu@shopee.com>
In-Reply-To: <ZAamFX/hq6Y/iNJb@casper.infradead.org>
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On 2023/3/7 10:48, Matthew Wilcox wrote:
> On Tue, Mar 07, 2023 at 10:36:55AM +0800, Haifeng Xu wrote:
>> On 2023/3/6 21:49, David Hildenbrand wrote:
>>> On 06.03.23 03:49, Haifeng Xu wrote:
>>>> mem_cgroup_oom_synchronize() has checked whether current memcg_in_oom is
>>>> set or not, so remove the check in handle_mm_fault().
>>>
>>> "mem_cgroup_oom_synchronize() will returned immediately if memcg_in_oom is not set, so remove the check from handle_mm_fault()".
>>>
>>> However, that requires now always an indirect function call -- do we care about dropping that optimization?
>>>
>>>
>>
>> If memcg_in_oom is set, we will check it twice, one is from handle_mm_fault(), the other is from mem_cgroup_oom_synchronize(). That seems a bit redundant.
>>
>> if memcg_in_oom is not set, mem_cgroup_oom_synchronize() returns directly. Though it's an indirect function call, but the time spent can be negligible 
>> compare to the whole mm user falut preocess. And that won't cause stack overflow error.
> 
> I suggest you measure it.

Ok, I'll make a simple test.