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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 56E1AC47247 for ; Mon, 4 May 2020 20:36:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 174D72073B for ; Mon, 4 May 2020 20:36:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="xsW3dOcn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 174D72073B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 952038E0080; Mon, 4 May 2020 16:36:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 903118E0058; Mon, 4 May 2020 16:36:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 83FD68E0080; Mon, 4 May 2020 16:36:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0009.hostedemail.com [216.40.44.9]) by kanga.kvack.org (Postfix) with ESMTP id 6C3068E0058 for ; Mon, 4 May 2020 16:36:06 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 2DDAC180AD80F for ; Mon, 4 May 2020 20:36:06 +0000 (UTC) X-FDA: 76780193532.08.ants64_5257ec700814c X-HE-Tag: ants64_5257ec700814c X-Filterd-Recvd-Size: 3963 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Mon, 4 May 2020 20:36:05 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AE292206A5; Mon, 4 May 2020 20:36:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588624564; bh=j+D4G91YVvT2I6r7MACf9KRILq64o0iwV58fg2WSfVM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xsW3dOcnob5j/K34MNs8HXTo/Ywd/2DNr1eZ+0Dujl+XoSormMaSrD0B/EWx/3bfm aYvgnj0F9yJZa1yaV4tNxCtKSB2NAntO04NOxUcnaF+uyDh907PivEwY6ndc3yrdxa o7/ut+jbYwCh1jnH/S5wzP5L5XxP1CZBRT7LVqSM= Date: Mon, 4 May 2020 13:36:04 -0700 From: Andrew Morton To: Mel Gorman Cc: Henry Willard , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: Limit boost_watermark on small zones. Message-Id: <20200504133604.5fd0b0b11b93bb4d9a0fed68@linux-foundation.org> In-Reply-To: <20200504124409.GB3758@techsingularity.net> References: <1588294148-6586-1-git-send-email-henry.willard@oracle.com> <20200501155729.a479c4b27f127d9aa866bd8e@linux-foundation.org> <20200504124409.GB3758@techsingularity.net> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 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?