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=-5.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 B960EC433E7 for ; Wed, 2 Sep 2020 14:55:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7D90E2078E for ; Wed, 2 Sep 2020 14:55:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D90E2078E 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 13A2A6B0083; Wed, 2 Sep 2020 10:55:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0EBB16B008A; Wed, 2 Sep 2020 10:55:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 000B36B008C; Wed, 2 Sep 2020 10:55:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0091.hostedemail.com [216.40.44.91]) by kanga.kvack.org (Postfix) with ESMTP id DDE286B0083 for ; Wed, 2 Sep 2020 10:55:08 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 82C0433CD for ; Wed, 2 Sep 2020 14:55:08 +0000 (UTC) X-FDA: 77218419096.30.join68_430ab9d270a1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 526A1180B3AA7 for ; Wed, 2 Sep 2020 14:55:07 +0000 (UTC) X-HE-Tag: join68_430ab9d270a1 X-Filterd-Recvd-Size: 2730 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Wed, 2 Sep 2020 14:55:06 +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 992D6AF3B; Wed, 2 Sep 2020 14:55:06 +0000 (UTC) Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline To: Pavel Tatashin , Michal Hocko Cc: LKML , Andrew Morton , linux-mm References: <20200901124615.137200-1-pasha.tatashin@soleen.com> <20200902140851.GJ4617@dhcp22.suse.cz> From: Vlastimil Babka Message-ID: <74f2341a-7834-3e37-0346-7fbc48d74df3@suse.cz> Date: Wed, 2 Sep 2020 16:55:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 526A1180B3AA7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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 9/2/20 4:26 PM, Pavel Tatashin wrote: > On Wed, Sep 2, 2020 at 10:08 AM Michal Hocko wrote: >> >> > >> > Thread#1 - continue >> > free_unref_page_commit >> > migratetype = get_pcppage_migratetype(page); >> > // get old migration type >> > list_add(&page->lru, &pcp->lists[migratetype]); >> > // add new page to already drained pcp list >> > >> > Thread#2 >> > Never drains pcp again, and therefore gets stuck in the loop. >> > >> > The fix is to try to drain per-cpu lists again after >> > check_pages_isolated_cb() fails. >> >> But this means that the page is not isolated and so it could be reused >> for something else. No? > > The page is in a movable zone, has zero references, and the section is > isolated (i.e. set_pageblock_migratetype(page, MIGRATE_ISOLATE);) is > set. The page should be offlinable, but it is lost in a pcp list as > that list is never drained again after the first failure to migrate > all pages in the range. Yeah. To answer Michal's "it could be reused for something else" - yes, somebody could allocate it from the pcplist before we do the extra drain. But then it becomes "visible again" and the loop in __offline_pages() should catch it by scan_movable_pages() - do_migrate_range(). And this time the pageblock is already marked as isolated, so the page (freed by migration) won't end up on the pcplist again.