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=-15.6 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=ham 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 859E0C433E0 for ; Fri, 5 Feb 2021 14:44:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DA6CE64E4E for ; Fri, 5 Feb 2021 14:44:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA6CE64E4E Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=virtuozzo.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 534AC6B0005; Fri, 5 Feb 2021 09:44:43 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4BE286B006C; Fri, 5 Feb 2021 09:44:43 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 310876B006E; Fri, 5 Feb 2021 09:44:43 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0054.hostedemail.com [216.40.44.54]) by kanga.kvack.org (Postfix) with ESMTP id 1736F6B0005 for ; Fri, 5 Feb 2021 09:44:43 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id CE5758249980 for ; Fri, 5 Feb 2021 14:44:42 +0000 (UTC) X-FDA: 77784485604.12.baby52_43048aa275e5 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id AC8C118025E9C for ; Fri, 5 Feb 2021 14:44:42 +0000 (UTC) X-HE-Tag: baby52_43048aa275e5 X-Filterd-Recvd-Size: 6339 Received: from relay.sw.ru (relay.sw.ru [185.231.240.75]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Fri, 5 Feb 2021 14:44:42 +0000 (UTC) Received: from [192.168.15.95] by relay.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1l82L1-001mbB-TC; Fri, 05 Feb 2021 17:43:59 +0300 Subject: Re: [v6 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers To: Yang Shi Cc: Roman Gushchin , Vlastimil Babka , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List References: <20210203172042.800474-1-shy828301@gmail.com> <20210203172042.800474-10-shy828301@gmail.com> <656865f5-bb56-4f4c-b88d-ec933a042b4c@virtuozzo.com> <5e335e4a-1556-e694-8f0b-192d924f99e5@virtuozzo.com> From: Kirill Tkhai Message-ID: Date: Fri, 5 Feb 2021 17:44:02 +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: 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 04.02.2021 20:32, Yang Shi wrote: > On Thu, Feb 4, 2021 at 2:14 AM Kirill Tkhai wrote: >> >> On 04.02.2021 12:29, Kirill Tkhai wrote: >>> 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(). >> >> I looked over my mail box, and I can't find that crash report and conditions to reproduce. >> >> Hm, let's remain this as is, and we rework this in case of such early shrinker call is still >> possible, and there will be a report... > > Sure. But I'm wondering how that could happen. On a very small machine? Sorry, but I don't remember. Maybe this case you said. Maybe some self-tests on node boot.. >> >> Reviewed-by: Kirill Tkhai >> >> With only nit: >> >>>> >>>> @@ -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); >> >> I've never seen return of void function in linux kernel. I'm not sure this won't confuse people. > > Will fix in v7. > >> >>>> >>>> kfree(shrinker->nr_deferred); >>>> shrinker->nr_deferred = NULL; >>>> >>> >> >>