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=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY, 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 6AD0BC388F9 for ; Wed, 11 Nov 2020 17:12:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C9F48206CA for ; Wed, 11 Nov 2020 17:12:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9F48206CA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3AE3B6B0036; Wed, 11 Nov 2020 12:12:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 35F0C6B006E; Wed, 11 Nov 2020 12:12:35 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 29C586B0070; Wed, 11 Nov 2020 12:12:35 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0158.hostedemail.com [216.40.44.158]) by kanga.kvack.org (Postfix) with ESMTP id F2BD56B0036 for ; Wed, 11 Nov 2020 12:12:34 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 96E4D181AEF07 for ; Wed, 11 Nov 2020 17:12:34 +0000 (UTC) X-FDA: 77472781428.13.roll28_5017d14272ff Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin13.hostedemail.com (Postfix) with ESMTP id 76FCF18140B69 for ; Wed, 11 Nov 2020 17:12:34 +0000 (UTC) X-HE-Tag: roll28_5017d14272ff X-Filterd-Recvd-Size: 4344 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Wed, 11 Nov 2020 17:12:33 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 51074AC24; Wed, 11 Nov 2020 17:12:32 +0000 (UTC) To: Alex Shi , akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com, willy@infradead.org, hannes@cmpxchg.org, lkp@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, shakeelb@google.com, iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com, kirill@shutemov.name, alexander.duyck@gmail.com, rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com, shy828301@gmail.com References: <1604566549-62481-1-git-send-email-alex.shi@linux.alibaba.com> <1604566549-62481-16-git-send-email-alex.shi@linux.alibaba.com> From: Vlastimil Babka Subject: Re: [PATCH v21 15/19] mm/compaction: do page isolation first in compaction Message-ID: Date: Wed, 11 Nov 2020 18:12:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <1604566549-62481-16-git-send-email-alex.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 11/5/20 9:55 AM, Alex Shi wrote: > Currently, compaction would get the lru_lock and then do page isolation > which works fine with pgdat->lru_lock, since any page isoltion would > compete for the lru_lock. If we want to change to memcg lru_lock, we > have to isolate the page before getting lru_lock, thus isoltion would > block page's memcg change which relay on page isoltion too. Then we > could safely use per memcg lru_lock later. >=20 > The new page isolation use previous introduced TestClearPageLRU() + > pgdat lru locking which will be changed to memcg lru lock later. >=20 > Hugh Dickins fixed following bugs in this patch's > early version: >=20 > Fix lots of crashes under compaction load: isolate_migratepages_block() > must clean up appropriately when rejecting a page, setting PageLRU agai= n > if it had been cleared; and a put_page() after get_page_unless_zero() > cannot safely be done while holding locked_lruvec - it may turn out to > be the final put_page(), which will take an lruvec lock when PageLRU. > And move __isolate_lru_page_prepare back after get_page_unless_zero to > make trylock_page() safe: > trylock_page() is not safe to use at this time: its setting PG_locked > can race with the page being freed or allocated ("Bad page"), and can > also erase flags being set by one of those "sole owners" of a freshly > allocated page who use non-atomic __SetPageFlag(). >=20 > Suggested-by: Johannes Weiner > Signed-off-by: Alex Shi > Acked-by: Hugh Dickins > Acked-by: Johannes Weiner > Cc: Andrew Morton > Cc: Matthew Wilcox > Cc: linux-kernel@vger.kernel.org > Cc: linux-mm@kvack.org Acked-by: Vlastimil Babka A question below: > @@ -979,10 +995,6 @@ static bool too_many_isolated(pg_data_t *pgdat) > goto isolate_abort; > } > =20 > - /* Recheck PageLRU and PageCompound under lock */ > - if (!PageLRU(page)) > - goto isolate_fail; > - > /* > * Page become compound since the non-locked check, > * and it's on LRU. It can only be a THP so the order > @@ -990,16 +1002,13 @@ static bool too_many_isolated(pg_data_t *pgdat) > */ > if (unlikely(PageCompound(page) && !cc->alloc_contig)) { > low_pfn +=3D compound_nr(page) - 1; > - goto isolate_fail; > + SetPageLRU(page); > + goto isolate_fail_put; > } IIUC the danger here is khugepaged will collapse a THP. For that,=20 __collapse_huge_page_isolate() has to succeed isolate_lru_page(). Under t= he new=20 scheme, it shouldn't be possible, right? If that's correct, we can remove= this part?