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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=unavailable 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 CD41BC282DA for ; Fri, 19 Apr 2019 18:21:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA404222AF for ; Fri, 19 Apr 2019 18:21:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727758AbfDSSVf (ORCPT ); Fri, 19 Apr 2019 14:21:35 -0400 Received: from outbound-smtp12.blacknight.com ([46.22.139.17]:46885 "EHLO outbound-smtp12.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727374AbfDSSVT (ORCPT ); Fri, 19 Apr 2019 14:21:19 -0400 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp12.blacknight.com (Postfix) with ESMTPS id 5855C1C333A for ; Fri, 19 Apr 2019 09:51:35 +0100 (IST) Received: (qmail 14374 invoked from network); 19 Apr 2019 08:51:35 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.225.79]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 19 Apr 2019 08:51:35 -0000 Date: Fri, 19 Apr 2019 09:51:33 +0100 From: Mel Gorman To: Andrew Morton Cc: Li Wang , Vlastimil Babka , linux-mm , linux-kernel@vger.kernel.org Subject: [PATCH] mm, page_alloc: Always use a captured page regardless of compaction result Message-ID: <20190419085133.GH18914@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org During the development of commit 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction"), a paranoid check was added to ensure that if a captured page was available after compaction that it was consistent with the final state of compaction. The intent was to catch serious programming bugs such as using a stale page pointer and causing corruption problems. However, it is possible to get a captured page even if compaction was unsuccessful if an interrupt triggered and happened to free pages in interrupt context that got merged into a suitable high-order page. It's highly unlikely but Li Wang did report the following warning on s390 occuring when testing OOM handling. Note that the warning is slightly edited for clarity. [ 1422.124060] WARNING: CPU: 0 PID: 9783 at mm/page_alloc.c:3777 __alloc_pages_direct_compact+0x182/0x190 [ 1422.124065] Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache sunrpc pkey ghash_s390 prng xts aes_s390 des_s390 des_generic sha512_s390 zcrypt_cex4 zcrypt vmur binfmt_misc ip_tables xfs libcrc32c dasd_fba_mod qeth_l2 dasd_eckd_mod dasd_mod qeth qdio lcs ctcm ccwgroup fsm dm_mirror dm_region_hash dm_log dm_mod [ 1422.124086] CPU: 0 PID: 9783 Comm: copy.sh Kdump: loaded Not tainted 5.1.0-rc 5 #1 This patch simply removes the check entirely instead of trying to be clever about pages freed from interrupt context. If a serious programming error was introduced, it is highly likely to be caught by prep_new_page() instead. Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction") Reported-by: Li Wang Signed-off-by: Mel Gorman --- mm/page_alloc.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d96ca5bc555b..cfaba3889fa2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3773,11 +3773,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, memalloc_noreclaim_restore(noreclaim_flag); psi_memstall_leave(&pflags); - if (*compact_result <= COMPACT_INACTIVE) { - WARN_ON_ONCE(page); - return NULL; - } - /* * At least in one zone compaction wasn't deferred or skipped, so let's * count a compaction stall