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Tue, 15 Dec 2020 03:05:33 +0000 (UTC) Received: from dread.disaster.area (pa49-179-6-140.pa.nsw.optusnet.com.au [49.179.6.140]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 60AA458C677; Tue, 15 Dec 2020 14:05:29 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1kp0eW-00454U-Mx; Tue, 15 Dec 2020 14:05:28 +1100 Date: Tue, 15 Dec 2020 14:05:28 +1100 From: Dave Chinner To: Yang Shi Cc: guro@fb.com, ktkhai@virtuozzo.com, shakeelb@google.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH 7/9] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Message-ID: <20201215030528.GN3913616@dread.disaster.area> References: <20201214223722.232537-1-shy828301@gmail.com> <20201214223722.232537-8-shy828301@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201214223722.232537-8-shy828301@gmail.com> X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=Ubgvt5aN c=1 sm=1 tr=0 cx=a_idp_d a=uDU3YIYVKEaHT0eX+MXYOQ==:117 a=uDU3YIYVKEaHT0eX+MXYOQ==:17 a=kj9zAlcOel0A:10 a=zTNgK-yGK50A:10 a=pGLkceISAAAA:8 a=7-415B0cAAAA:8 a=HoWvQtbgcFNr9bk3r4sA:9 a=CjuIK1q_8ugA:10 a=-RoEEKskQ1sA:10 a=biEYGPWJfzWAr4FL6Ov7:22 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 Mon, Dec 14, 2020 at 02:37:20PM -0800, Yang Shi wrote: > Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need > allocate shrinker->nr_deferred for such shrinkers anymore. > > Signed-off-by: Yang Shi > --- > mm/vmscan.c | 28 ++++++++++++++-------------- > 1 file changed, 14 insertions(+), 14 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bce8cf44eca2..8d5bfd818acd 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -420,7 +420,15 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone > */ > int prealloc_shrinker(struct shrinker *shrinker) > { > - unsigned int size = sizeof(*shrinker->nr_deferred); > + unsigned int size; > + > + if (is_deferred_memcg_aware(shrinker)) { > + if (prealloc_memcg_shrinker(shrinker)) > + return -ENOMEM; > + return 0; > + } > + > + size = sizeof(*shrinker->nr_deferred); > > if (shrinker->flags & SHRINKER_NUMA_AWARE) > size *= nr_node_ids; > @@ -429,26 +437,18 @@ int prealloc_shrinker(struct shrinker *shrinker) > if (!shrinker->nr_deferred) > return -ENOMEM; > > - if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > - if (prealloc_memcg_shrinker(shrinker)) > - goto free_deferred; > - } > - > return 0; > - > -free_deferred: > - kfree(shrinker->nr_deferred); > - shrinker->nr_deferred = NULL; > - return -ENOMEM; > } I'm trying to put my finger on it, but this seems wrong to me. If memcgs are disabled, then prealloc_memcg_shrinker() needs to fail. The preallocation code should not care about internal memcg details like this. /* * If the shrinker is memcg aware and memcgs are not * enabled, clear the MEMCG flag and fall back to non-memcg * behaviour for the shrinker. */ if (shrinker->flags & SHRINKER_MEMCG_AWARE) { error = prealloc_memcg_shrinker(shrinker); if (!error) return 0; if (error != -ENOSYS) return error; /* memcgs not enabled! */ shrinker->flags &= ~SHRINKER_MEMCG_AWARE; } size = sizeof(*shrinker->nr_deferred); .... return 0; } This guarantees that only the shrinker instances taht have a correctly set up memcg attached to them will have the SHRINKER_MEMCG_AWARE flag set. Hence in all the rest of the shrinker code, we only ever need to check for SHRINKER_MEMCG_AWARE to determine what we should do.... > void free_prealloced_shrinker(struct shrinker *shrinker) > { > - if (!shrinker->nr_deferred) > + if (is_deferred_memcg_aware(shrinker)) { > + unregister_memcg_shrinker(shrinker); > return; > + } > > - if (shrinker->flags & SHRINKER_MEMCG_AWARE) > - unregister_memcg_shrinker(shrinker); > + if (!shrinker->nr_deferred) > + return; > > kfree(shrinker->nr_deferred); > shrinker->nr_deferred = NULL; e.g. then this function can simply do: { if (shrinker->flags & SHRINKER_MEMCG_AWARE) return unregister_memcg_shrinker(shrinker); kfree(shrinker->nr_deferred); shrinker->nr_deferred = NULL; } Cheers, Dave. -- Dave Chinner david@fromorbit.com