From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44349C433E0 for ; Mon, 11 Jan 2021 21:58:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B95C22CB8 for ; Mon, 11 Jan 2021 21:58:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387864AbhAKV6x (ORCPT ); Mon, 11 Jan 2021 16:58:53 -0500 Received: from relay.sw.ru ([185.231.240.75]:60986 "EHLO relay3.sw.ru" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728040AbhAKV6w (ORCPT ); Mon, 11 Jan 2021 16:58:52 -0500 Received: from [192.168.15.62] by relay3.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1kz5BG-00GEv4-Ka; Tue, 12 Jan 2021 00:56:54 +0300 Subject: Re: [v3 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers To: Yang Shi Cc: Roman Gushchin , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List References: <20210105225817.1036378-1-shy828301@gmail.com> <20210105225817.1036378-10-shy828301@gmail.com> <7c591313-08fd-4f98-6021-6dfa59f01aff@virtuozzo.com> From: Kirill Tkhai Message-ID: Date: Tue, 12 Jan 2021 00:57:02 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.01.2021 21:40, Yang Shi wrote: > On Wed, Jan 6, 2021 at 3:16 AM Kirill Tkhai wrote: >> >> 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: > > Not only !CONFIG_MEMCG, but also "cgroup_disable=memory" case. > >> >> #ifdef CONFIG_MEMCG >> #define SHRINKER_MEMCG_AWARE (1 << 2) >> #else >> #define SHRINKER_MEMCG_AWARE 0 >> #endif > > This could handle !CONFIG_MEMCG case, but can't deal with > "cgroup_disable=memory" case. We could consider check > mem_cgroup_disabled() when initializing shrinker, but this may result > in touching fs codes like below: > > --- a/fs/super.c > +++ b/fs/super.c > @@ -266,7 +266,9 @@ static struct super_block *alloc_super(struct > file_system_type *type, int flags, > s->s_shrink.scan_objects = super_cache_scan; > s->s_shrink.count_objects = super_cache_count; > s->s_shrink.batch = 1024; > - s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE; > + s->s_shrink.flags = SHRINKER_NUMA_AWARE; > + if (!mem_cgroup_disabled()) > + s->s_shrink.flags |= SHRINKER_MEMCG_AWARE; > if (prealloc_shrinker(&s->s_shrink)) > goto fail; > if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink)) Oh. If so, then initial variant was better. >> >>> + } >>> >>> + 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; >>> >> >>