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 62BFDC77B7F for ; Thu, 18 May 2023 01:22:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229635AbjERBWs (ORCPT ); Wed, 17 May 2023 21:22:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbjERBWq (ORCPT ); Wed, 17 May 2023 21:22:46 -0400 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3257130E4 for ; Wed, 17 May 2023 18:22:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1684372965; x=1715908965; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=kvsuCZV5nRL+RW1S2zTLxwGX75/5cDfIVioej0JSzEk=; b=aC4ftNVGiE60G6gvUjOH24mpx5KZSNo5jCFNMVKhqfF3yKTTcQ5tWZcL upGKO4slNMAYOzOWTM9ttYikssAuZjyVBiNNNprBknA5ChL0Ng4HCHJ20 wSCM1BOrKCsvQmuPic6ybdGC0ABSJSJ5Nh3KaKGBH88KdQ3agReaDfRK4 kyZ4n67Ql2f9RQOYE01ppjFThZB+DZt6Vyr/J2hbapG+J7gi+dlLS/KVX 8Bkn6spWphHjeF75ByLTvMG3krTt79BYhvCQvcBg3VlusHx8Ymv/hFzP8 VWcFNkD5npByo1y1MfgTVKoqsojPMpNS5287NYSgDAV62eSbdlxg9LjqK Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10713"; a="341327661" X-IronPort-AV: E=Sophos;i="5.99,283,1677571200"; d="scan'208";a="341327661" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 May 2023 18:22:44 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10713"; a="679493595" X-IronPort-AV: E=Sophos;i="5.99,283,1677571200"; d="scan'208";a="679493595" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 May 2023 18:22:42 -0700 From: "Huang, Ying" To: Khalid Aziz Cc: akpm@linux-foundation.org, willy@infradead.org, steven.sistare@oracle.com, mgorman@techsingularity.net, khalid@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm, compaction: Skip all non-migratable pages during scan References: <20230517161555.84776-1-khalid.aziz@oracle.com> Date: Thu, 18 May 2023 09:21:39 +0800 In-Reply-To: <20230517161555.84776-1-khalid.aziz@oracle.com> (Khalid Aziz's message of "Wed, 17 May 2023 10:15:54 -0600") Message-ID: <87o7mibfj0.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Khalid Aziz writes: > 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 appears duplicated with the comments in caller. It's OK to keep one only? > + * 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() It's not good to duplicate code. Why not just use folio_expected_refs()? Best Regards, Huang, Ying > + */ > +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)) > + 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; > > /*