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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 0CB22C33CB1 for ; Fri, 17 Jan 2020 09:26:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 993C22082F for ; Fri, 17 Jan 2020 09:26:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 993C22082F Authentication-Results: mail.kernel.org; dmarc=fail (p=none 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 382936B033A; Fri, 17 Jan 2020 04:26:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 333296B033B; Fri, 17 Jan 2020 04:26:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2497C6B033D; Fri, 17 Jan 2020 04:26:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0223.hostedemail.com [216.40.44.223]) by kanga.kvack.org (Postfix) with ESMTP id 0FC4C6B033A for ; Fri, 17 Jan 2020 04:26:34 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id BCBFA180AD806 for ; Fri, 17 Jan 2020 09:26:33 +0000 (UTC) X-FDA: 76386595866.09.alarm94_1c15d04eee720 X-HE-Tag: alarm94_1c15d04eee720 X-Filterd-Recvd-Size: 5681 Received: from relay.sw.ru (relay.sw.ru [185.231.240.75]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Fri, 17 Jan 2020 09:26:32 +0000 (UTC) Received: from dhcp-172-16-24-104.sw.ru ([172.16.24.104]) by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1isNtV-0005s1-FT; Fri, 17 Jan 2020 12:26:21 +0300 Subject: Re: [Patch v3] mm: thp: grab the lock before manipulation defer list To: Michal Hocko , David Rientjes Cc: Wei Yang , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, alexander.duyck@gmail.com, stable@vger.kernel.org References: <20200116013100.7679-1-richardw.yang@linux.intel.com> <0bb34c4a-97c7-0b3c-cf43-8af6cf9c4396@virtuozzo.com> <20200117091002.GM19428@dhcp22.suse.cz> From: Kirill Tkhai Message-ID: Date: Fri, 17 Jan 2020 12:26:20 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200117091002.GM19428@dhcp22.suse.cz> 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 17.01.2020 12:10, Michal Hocko wrote: > On Thu 16-01-20 14:01:59, David Rientjes wrote: >> On Thu, 16 Jan 2020, Kirill Tkhai wrote: >> >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index c5b5f74cfd4d..6450bbe394e2 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -5360,10 +5360,12 @@ static int (struct page *page, >>>> } >>>> >>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>> - if (compound && !list_empty(page_deferred_list(page))) { >>>> + if (compound) { >>>> spin_lock(&from->deferred_split_queue.split_queue_lock); >>>> - list_del_init(page_deferred_list(page)); >>>> - from->deferred_split_queue.split_queue_len--; >>>> + if (!list_empty(page_deferred_list(page))) { >>>> + list_del_init(page_deferred_list(page)); >>>> + from->deferred_split_queue.split_queue_len--; >>>> + } >>>> spin_unlock(&from->deferred_split_queue.split_queue_lock); >>>> } >>>> #endif >>>> @@ -5377,11 +5379,13 @@ static int mem_cgroup_move_account(struct page *page, >>>> page->mem_cgroup = to; >>>> >>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>> - if (compound && list_empty(page_deferred_list(page))) { >>>> + if (compound) { >>>> spin_lock(&to->deferred_split_queue.split_queue_lock); >>>> - list_add_tail(page_deferred_list(page), >>>> - &to->deferred_split_queue.split_queue); >>>> - to->deferred_split_queue.split_queue_len++; >>>> + if (list_empty(page_deferred_list(page))) { >>>> + list_add_tail(page_deferred_list(page), >>>> + &to->deferred_split_queue.split_queue); >>>> + to->deferred_split_queue.split_queue_len++; >>>> + } >>>> spin_unlock(&to->deferred_split_queue.split_queue_lock); >>>> } >>>> #endif >>> >>> The patch looks OK for me. But there is another question. I forget, why we unconditionally >>> add a page with empty deferred list to deferred_split_queue. Shouldn't we also check that >>> it was initially in the list? Something like: >>> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index d4394ae4e5be..0be0136adaa6 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -5289,6 +5289,7 @@ static int mem_cgroup_move_account(struct page *page, >>> struct pglist_data *pgdat; >>> unsigned long flags; >>> unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1; >>> + bool split = false; >>> int ret; >>> bool anon; >>> >>> @@ -5346,6 +5347,7 @@ static int mem_cgroup_move_account(struct page *page, >>> if (!list_empty(page_deferred_list(page))) { >>> list_del_init(page_deferred_list(page)); >>> from->deferred_split_queue.split_queue_len--; >>> + split = true; >>> } >>> spin_unlock(&from->deferred_split_queue.split_queue_lock); >>> } >>> @@ -5360,7 +5362,7 @@ static int mem_cgroup_move_account(struct page *page, >>> page->mem_cgroup = to; >>> >>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> - if (compound) { >>> + if (compound && split) { >>> spin_lock(&to->deferred_split_queue.split_queue_lock); >>> if (list_empty(page_deferred_list(page))) { >>> list_add_tail(page_deferred_list(page), >>> >> >> I think that's a good point, especially considering that the current code >> appears to unconditionally place any compound page on the deferred split >> queue of the destination memcg. The correct list that it should appear >> on, I believe, depends on whether the pmd has been split for the process >> being moved: note the MC_TARGET_PAGE caveat in >> mem_cgroup_move_charge_pte_range() that does not move the charge for >> compound pages with split pmds. So when mem_cgroup_move_account() is >> called with compound == true, we're moving the charge of the entire >> compound page: why would it appear on that memcg's deferred split queue? > > I believe Kirill asked how do we know that the page should be actually > added to the deferred list just from the list_empty check. In other > words what if the page hasn't been split at all? Yes, I'm talking about this. Function mem_cgroup_move_account() adds every huge page to the deferred list, while we need to do that only for pages, which are queued for splitting...