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Thu, 4 Feb 2021 09:30:24 +0000 (UTC) Received: from [192.168.15.247] by relay.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1l7axL-001fKb-Hd; Thu, 04 Feb 2021 12:29:43 +0300 Subject: Re: [v6 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers To: Yang Shi , guro@fb.com, vbabka@suse.cz, shakeelb@google.com, david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210203172042.800474-1-shy828301@gmail.com> <20210203172042.800474-10-shy828301@gmail.com> From: Kirill Tkhai Message-ID: <656865f5-bb56-4f4c-b88d-ec933a042b4c@virtuozzo.com> Date: Thu, 4 Feb 2021 12:29:43 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210203172042.800474-10-shy828301@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 03.02.2021 20:20, 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. > > The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled > by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared. > This makes the implementation of this patch simpler. > > Acked-by: Vlastimil Babka > Signed-off-by: Yang Shi > --- > mm/vmscan.c | 31 ++++++++++++++++--------------- > 1 file changed, 16 insertions(+), 15 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 545422d2aeec..20a35d26ae12 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -334,6 +334,9 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker) > { > int id, ret = -ENOMEM; > > + if (mem_cgroup_disabled()) > + return -ENOSYS; > + > down_write(&shrinker_rwsem); > /* This may call shrinker, so it must use down_read_trylock() */ > id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); > @@ -414,7 +417,7 @@ static bool writeback_throttling_sane(struct scan_control *sc) > #else > static int prealloc_memcg_shrinker(struct shrinker *shrinker) > { > - return 0; > + return -ENOSYS; > } > > static void unregister_memcg_shrinker(struct shrinker *shrinker) > @@ -525,8 +528,18 @@ 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; > + int err; > + > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > + err = prealloc_memcg_shrinker(shrinker); > + if (err != -ENOSYS) > + return err; > > + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; > + } > + > + size = sizeof(*shrinker->nr_deferred); > if (shrinker->flags & SHRINKER_NUMA_AWARE) > size *= nr_node_ids; This may sound surprisingly, but IIRC do_shrink_slab() may be called on early boot *even before* root_mem_cgroup is allocated. AFAIR, I received syzcaller crash report because of this, when I was implementing shrinker_maps. This is a reason why we don't use shrinker_maps even in case of mem cgroup is not disabled: we iterate every shrinker of shrinker_list. See check in shrink_slab(): if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) Possible, we should do the same for nr_deferred: 1)always allocate shrinker->nr_deferred, 2)use shrinker->nr_deferred in count_nr_deferred() and set_nr_deferred(). > > @@ -534,26 +547,14 @@ 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; > } > > void free_prealloced_shrinker(struct shrinker *shrinker) > { > - if (!shrinker->nr_deferred) > - return; > - > if (shrinker->flags & SHRINKER_MEMCG_AWARE) > - unregister_memcg_shrinker(shrinker); > + return unregister_memcg_shrinker(shrinker); > > kfree(shrinker->nr_deferred); > shrinker->nr_deferred = NULL; >