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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 B31C6C47254 for ; Tue, 5 May 2020 07:58:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 559DC20658 for ; Tue, 5 May 2020 07:58:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 559DC20658 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C5C788E009E; Tue, 5 May 2020 03:58:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BE6088E0058; Tue, 5 May 2020 03:58:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AFD3C8E009E; Tue, 5 May 2020 03:58:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0143.hostedemail.com [216.40.44.143]) by kanga.kvack.org (Postfix) with ESMTP id 953518E0058 for ; Tue, 5 May 2020 03:58:36 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 465A118ED7 for ; Tue, 5 May 2020 07:58:36 +0000 (UTC) X-FDA: 76781913432.15.bat87_4b0964ffcfc18 X-HE-Tag: bat87_4b0964ffcfc18 X-Filterd-Recvd-Size: 4383 Received: from outbound-smtp03.blacknight.com (outbound-smtp03.blacknight.com [81.17.249.16]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Tue, 5 May 2020 07:58:35 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp03.blacknight.com (Postfix) with ESMTPS id E79FBC13E3 for ; Tue, 5 May 2020 08:58:33 +0100 (IST) Received: (qmail 11419 invoked from network); 5 May 2020 07:58:33 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.18.57]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 5 May 2020 07:58:33 -0000 Date: Tue, 5 May 2020 08:58:31 +0100 From: Mel Gorman To: Andrew Morton Cc: Henry Willard , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: Limit boost_watermark on small zones. Message-ID: <20200505075831.GC3758@techsingularity.net> References: <1588294148-6586-1-git-send-email-henry.willard@oracle.com> <20200501155729.a479c4b27f127d9aa866bd8e@linux-foundation.org> <20200504124409.GB3758@techsingularity.net> <20200504133604.5fd0b0b11b93bb4d9a0fed68@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20200504133604.5fd0b0b11b93bb4d9a0fed68@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Mon, May 04, 2020 at 01:36:04PM -0700, Andrew Morton wrote: > On Mon, 4 May 2020 13:44:09 +0100 Mel Gorman wrote: > > > On Fri, May 01, 2020 at 03:57:29PM -0700, Andrew Morton wrote: > > > On Thu, 30 Apr 2020 17:49:08 -0700 Henry Willard wrote: > > > > > > > Commit 1c30844d2dfe ("mm: reclaim small amounts of memory when an external > > > > fragmentation event occurs") adds a boost_watermark() function which > > > > increases the min watermark in a zone by at least pageblock_nr_pages or > > > > the number of pages in a page block. On Arm64, with 64K pages and 512M > > > > huge pages, this is 8192 pages or 512M. It does this regardless of the > > > > number of managed pages managed in the zone or the likelihood of success. > > > > This can put the zone immediately under water in terms of allocating pages > > > > from the zone, and can cause a small machine to fail immediately due to > > > > OoM. Unlike set_recommended_min_free_kbytes(), which substantially > > > > increases min_free_kbytes and is tied to THP, boost_watermark() can be > > > > called even if THP is not active. The problem is most likely to appear > > > > on architectures such as Arm64 where pageblock_nr_pages is very large. > > > > > > > > It is desirable to run the kdump capture kernel in as small a space as > > > > possible to avoid wasting memory. In some architectures, such as Arm64, > > > > there are restrictions on where the capture kernel can run, and therefore, > > > > the space available. A capture kernel running in 768M can fail due to OoM > > > > immediately after boost_watermark() sets the min in zone DMA32, where > > > > most of the memory is, to 512M. It fails even though there is over 500M of > > > > free memory. With boost_watermark() suppressed, the capture kernel can run > > > > successfully in 448M. > > > > > > > > This patch limits boost_watermark() to boosting a zone's min watermark only > > > > when there are enough pages that the boost will produce positive results. > > > > In this case that is estimated to be four times as many pages as > > > > pageblock_nr_pages. > > > > > > > > > ... > > Acked-by: Mel Gorman > > Cool. I wonder if we should backport this into -stable kernels? "can > cause a small machine to fail immediately" sounds serious, but > 1c30844d2dfe is from December 2018. Any thoughts? There is no harm in marking it stable. Clearly it does not happen very often but it's not impossible. 32-bit x86 is a lot less common now which would previously have been vulnerable to triggering this easily. ppc64 has a larger base page size but typically only has one zone. arm64 is likely the most vulnerable, particularly when CMA is configured with a small movable zone. -- Mel Gorman SUSE Labs