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=-2.3 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 31B3AC3A5A9 for ; Mon, 4 May 2020 12:52:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A596206D9 for ; Mon, 4 May 2020 12:52:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728937AbgEDMww (ORCPT ); Mon, 4 May 2020 08:52:52 -0400 Received: from outbound-smtp09.blacknight.com ([46.22.139.14]:55489 "EHLO outbound-smtp09.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726404AbgEDMwv (ORCPT ); Mon, 4 May 2020 08:52:51 -0400 X-Greylist: delayed 518 seconds by postgrey-1.27 at vger.kernel.org; Mon, 04 May 2020 08:52:50 EDT Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp09.blacknight.com (Postfix) with ESMTPS id 538B61C3C52 for ; Mon, 4 May 2020 13:44:11 +0100 (IST) Received: (qmail 21279 invoked from network); 4 May 2020 12:44:11 -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); 4 May 2020 12:44:11 -0000 Date: Mon, 4 May 2020 13:44:09 +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: <20200504124409.GB3758@techsingularity.net> References: <1588294148-6586-1-git-send-email-henry.willard@oracle.com> <20200501155729.a479c4b27f127d9aa866bd8e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20200501155729.a479c4b27f127d9aa866bd8e@linux-foundation.org> 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 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. > > > > Let's Cc Mel. > Seems reasonable. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs