Date:   Tue, 7 Mar 2023 02:48:53 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Haifeng Xu <haifeng.xu@shopee.com>
Cc:     David Hildenbrand <david@redhat.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: remove redundant check in handle_mm_fault
Message-ID: <ZAamFX/hq6Y/iNJb@casper.infradead.org>
References: <20230306024959.131468-1-haifeng.xu@shopee.com>
 <df3997ed-a844-597b-fbb1-154caad78543@redhat.com>
 <354360d5-dce6-a11c-ee61-d41e615bfa05@shopee.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <354360d5-dce6-a11c-ee61-d41e615bfa05@shopee.com>
Precedence: bulk

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.