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Wed, 6 Jan 2021 11:15:58 +0000 (UTC) Received: from [192.168.15.143] by relay3.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1kx6mG-00Fd6I-Ge; Wed, 06 Jan 2021 14:14:56 +0300 Subject: Re: [v3 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers To: Yang Shi , guro@fb.com, 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: <20210105225817.1036378-1-shy828301@gmail.com> <20210105225817.1036378-10-shy828301@gmail.com> From: Kirill Tkhai Message-ID: <7c591313-08fd-4f98-6021-6dfa59f01aff@virtuozzo.com> Date: Wed, 6 Jan 2021 14:15:07 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210105225817.1036378-10-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 06.01.2021 01:58, 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. > > Signed-off-by: Yang Shi > --- > mm/vmscan.c | 33 ++++++++++++++++++--------------- > 1 file changed, 18 insertions(+), 15 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f20ed8e928c2..d9795fb0f1c5 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -340,6 +340,9 @@ 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_REGISTERING, 0, 0, GFP_KERNEL); > @@ -424,7 +427,7 @@ 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) > @@ -535,8 +538,20 @@ 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) > + return 0; > + if (err != -ENOSYS) > + return err; > + > + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; This looks very confusing. In case of you want to disable preallocation branch for !MEMCG case, you should firstly consider something like the below: #ifdef CONFIG_MEMCG #define SHRINKER_MEMCG_AWARE (1 << 2) #else #define SHRINKER_MEMCG_AWARE 0 #endif > + } > > + size = sizeof(*shrinker->nr_deferred); > if (shrinker->flags & SHRINKER_NUMA_AWARE) > size *= nr_node_ids; > > @@ -544,26 +559,14 @@ 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; >