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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55BF1C77B75 for ; Tue, 23 May 2023 03:42:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232394AbjEWDmc (ORCPT ); Mon, 22 May 2023 23:42:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46144 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232594AbjEWDm1 (ORCPT ); Mon, 22 May 2023 23:42:27 -0400 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 80FB394 for ; Mon, 22 May 2023 20:42:24 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046056;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0VjIRpOt_1684813339; Received: from 30.97.48.45(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VjIRpOt_1684813339) by smtp.aliyun-inc.com; Tue, 23 May 2023 11:42:20 +0800 Message-ID: <4453e142-f2c5-7016-acc0-3c861b8d0a0d@linux.alibaba.com> Date: Tue, 23 May 2023 11:42:34 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v3] mm, compaction: Skip all non-migratable pages during scan To: Khalid Aziz , akpm@linux-foundation.org Cc: willy@infradead.org, steven.sistare@oracle.com, ying.huang@intel.com, mgorman@techsingularity.net, khalid@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230517161555.84776-1-khalid.aziz@oracle.com> From: Baolin Wang In-Reply-To: <20230517161555.84776-1-khalid.aziz@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/18/2023 12:15 AM, Khalid Aziz wrote: > Pages pinned in memory through extra refcounts can not be migrated. > Currently as isolate_migratepages_block() scans pages for > compaction, it skips any pinned anonymous pages. All non-migratable > pages should be skipped and not just the anonymous pinned pages. > This patch adds a check for extra refcounts on a page to determine > if the page can be migrated. This was seen as a real issue on a > customer workload where a large number of pages were pinned by vfio > on the host and any attempts to allocate hugepages resulted in > significant amount of cpu time spent in either direct compaction or > in kcompactd scanning vfio pinned pages over and over again that can > not be migrated. > > Signed-off-by: Khalid Aziz > Suggested-by: Steve Sistare > --- > v3: > - Account for extra ref added by get_page_unless_zero() earlier > in isolate_migratepages_block() (Suggested by Huang, Ying) > - Clean up computation of extra refs to be consistent > (Suggested by Huang, Ying) > > v2: > - Update comments in the code (Suggested by Andrew) > - Use PagePrivate() instead of page_has_private() (Suggested > by Matthew) > - Pass mapping to page_has_extrarefs() (Suggested by Matthew) > - Use page_ref_count() (Suggested by Matthew) > - Rename is_pinned_page() to reflect its function more > accurately (Suggested by Matthew) > > mm/compaction.c | 36 ++++++++++++++++++++++++++++++++---- > 1 file changed, 32 insertions(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 5a9501e0ae01..f04c00981172 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -764,6 +764,34 @@ static bool too_many_isolated(pg_data_t *pgdat) > return too_many; > } > > +/* > + * Check if this base page should be skipped from isolation because > + * it has extra refcounts that will prevent it from being migrated. > + * This function is called for regular pages only, and not > + * for THP or hugetlbfs pages. This code is inspired by similar code > + * in migrate_vma_check_page(), can_split_folio() and > + * folio_migrate_mapping() > + */ > +static inline bool page_has_extra_refs(struct page *page) > +{ > + /* caller holds a ref already from get_page_unless_zero() */ > + unsigned long extra_refs = 1; > + > + /* anonymous page can have extra ref from swap cache */ > + if (PageAnon(page)) > + extra_refs += PageSwapCache(page) ? 1 : 0; > + else > + extra_refs += 1 + PagePrivate(page); > + > + /* > + * This is an admittedly racy check but good enough to determine > + * if a page is pinned and can not be migrated > + */ > + if ((page_ref_count(page) - extra_refs) > page_mapcount(page)) Could you explain why changing total_mapcount() to page_mapcount()? The original commit 829ae0f81ce0 ("mm: migrate: fix THP's mapcount on isolation") did fix a THP's mapcount issue with converting to total_mapcount(). > + return true; > + return false; > +} > + > /** > * isolate_migratepages_block() - isolate all migrate-able pages within > * a single pageblock > @@ -992,12 +1020,12 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > goto isolate_fail; > > /* > - * Migration will fail if an anonymous page is pinned in memory, > - * so avoid taking lru_lock and isolating it unnecessarily in an > - * admittedly racy check. > + * Migration will fail if a page has extra refcounts > + * preventing it from migrating, so avoid taking > + * lru_lock and isolating it unnecessarily > */ > mapping = page_mapping(page); > - if (!mapping && (page_count(page) - 1) > total_mapcount(page)) > + if (page_has_extra_refs(page)) > goto isolate_fail_put; > > /*