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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id i10sm12343249wru.16.2019.12.05.03.45.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Dec 2019 03:45:22 -0800 (PST) Date: Thu, 5 Dec 2019 12:45:21 +0100 From: Michal Hocko To: Kirill Tkhai Cc: Yang Shi , hannes@cmpxchg.org, shakeelb@google.com, guro@fb.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: vmscan: protect shrinker idr replace with CONFIG_MEMCG Message-ID: <20191205114521.GF28317@dhcp22.suse.cz> References: <1575486978-45249-1-git-send-email-yang.shi@linux.alibaba.com> <20191205094341.GC28317@dhcp22.suse.cz> <894b9951-449d-6d7e-84aa-a1c510417710@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <894b9951-449d-6d7e-84aa-a1c510417710@virtuozzo.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 05-12-19 13:00:31, Kirill Tkhai wrote: > On 05.12.2019 12:43, Michal Hocko wrote: > > On Thu 05-12-19 11:23:28, Kirill Tkhai wrote: > >> On 04.12.2019 22:16, Yang Shi wrote: > >>> Since commit 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: > >>> make shrinker not depend on memcg kmem"), shrinkers' idr is protected by > >>> CONFIG_MEMCG instead of CONFIG_MEMCG_KMEM, so it makes no sense to > >>> protect shrinker idr replace with CONFIG_MEMCG_KMEM. > >>> > >>> Cc: Kirill Tkhai > >>> Cc: Johannes Weiner > >>> Cc: Michal Hocko > >>> Cc: Shakeel Butt > >>> Cc: Roman Gushchin > >>> Signed-off-by: Yang Shi > >> > >> It looks like that in CONFIG_SLOB case we do not even call some shrinkers > >> for subordinate mem cgroups (i.e., we don't call deferred_split_shrinker), > >> since they never become completely registered. > >> > >> Fixes: 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 ("mm: shrinker: make shrinker not depend on memcg kmem") > > > > I am confused. Why the Fixes tag? Nothing should be really broken with > > KMEM config guard right? > > idr_replace() is disabled in CONFIG_MEMCG && CONFIG_SLOB case, and this is > wrong. > > 0a432dcbeb32edcd211a5d8f7847d0da7642a8b4 goes in the series, which enables > shrinker_idr infrastructure for huge_memory.c's deferred_split_shrinker > in CONFIG_MEMCG case. Previously, all SHRINKER_MEMCG_AWARE shrinkers were > based on LRUs, and they remain to base of CONFIG_MEMCG_KMEM. > But deferred_split_shrinker is an exception. > > In CONFIG_MEMCG && CONFIG_SLOB case, shrinker_idr contains only shrinker, > and it is deferred_split_shrinker. But it is never actually called, since > idr_replace() is never compiled. deferred_split_shrinker all the time is > staying in half-registered state, and it's never called for subordinate > mem cgroups. > > So, this is a BUG, and this should go to stable. OK, I see. The changelog should describe all that. Thanks for the clarification. > > This is a mere clean up AFAICS. > > > >> Reviewed-by: Kirill Tkhai > >> > >>> --- > >>> mm/vmscan.c | 2 +- > >>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>> > >>> diff --git a/mm/vmscan.c b/mm/vmscan.c > >>> index ee4eecc..e7f10c4 100644 > >>> --- a/mm/vmscan.c > >>> +++ b/mm/vmscan.c > >>> @@ -422,7 +422,7 @@ void register_shrinker_prepared(struct shrinker *shrinker) > >>> { > >>> down_write(&shrinker_rwsem); > >>> list_add_tail(&shrinker->list, &shrinker_list); > >>> -#ifdef CONFIG_MEMCG_KMEM > >>> +#ifdef CONFIG_MEMCG > >>> if (shrinker->flags & SHRINKER_MEMCG_AWARE) > >>> idr_replace(&shrinker_idr, shrinker, shrinker->id); > >>> #endif > >>> > > > -- Michal Hocko SUSE Labs