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s=korg; t=1681934592; bh=Jfd6Xw8NQMQFh3SvgGvyWz47eLEspURjqLTeUCEqvR4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=vRCaoOzyYQozupKl9cnrLB0UfnuK3KJXN7MCcTdViQpst9lNJ52INEF5T6j0m8XDx 2AFs2oGpOrpZFyFkaS25uhRF7U25nPk1KZcYLOOMlhhLEKclcsbOdsH+dZIzFMJS6e 9yvdiL6SPO0eW4jzmKhJI+mXR0hGM4lCI6uqgJdU= Date: Wed, 19 Apr 2023 13:03:11 -0700 From: Andrew Morton To: Haifeng Xu 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() Message-Id: <20230419130311.587b7273eca2512c07b32bd0@linux-foundation.org> In-Reply-To: <20230419092007.186938-1-haifeng.xu@shopee.com> References: <20230419092007.186938-1-haifeng.xu@shopee.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 2CBF0180010 X-Rspamd-Server: rspam09 X-Stat-Signature: 7it3cuwzs4a6s8sdc53f89r3jinbudiu X-HE-Tag: 1681934593-324953 X-HE-Meta: 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 UUN9pmWW Hv3Ugq961eJzifnSBIhLwdTiJFdEbQPrtMKye2HzBlsZBczpagycqPM//ZGtQ/Brzbp8tGvkbsR4W/Gvh6+NDXO48QqTrtM31dhtoBDPfNrom1dUuyjZ13/bKC2xXZDVOzeZ+1Fg1XuKIMpHL0uVSCAaIdJpParS7RLP1h/DTrdYlHXBZY7hShfSrrN+GhTaCQ0iAhwmaGJVv6DqKjQmWWzfWjShXni84Sdy93MX70ub/PwdEFPKOgNOM6YKqWh5TfrIogB/mF3UJp4fWXQ+oQw3SYWgmBWdPYFWcMgdvKS4/D+hygx/2M8a+0KFkxi85By+iqdNui9pAeR4APtyhvOFx/gwTIJg5k8bPfWTkeDrkR+zFsOSKOJOKh2ZbKm+1VIujwPPplJMMFeZue/C0zjow5Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 19 Apr 2023 09:20:07 +0000 Haifeng Xu 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? 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.