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 60744C47256 for ; Fri, 1 May 2020 22:57:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 32ED2216FD for ; Fri, 1 May 2020 22:57:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588373852; bh=LXBvB44SCeNdj+HATb89++1mLFiPdFO5sDwPGdqjuAU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=r1CLNvMloX7wPzv60YPTUzqqOrWhegBzTgkpPHiIs1ya5vvnCT1UkoH8RX98wCgU4 6yM50DC7kA6GATWEdExRIs2rYVDReSMQBtf1bevcqmE9Y/qIN0j41xQk6fTjrh+aJz 57R/06QDs8QMs9jFEmS+IVDSAdF77aao1jsr5dvk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726784AbgEAW5b (ORCPT ); Fri, 1 May 2020 18:57:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:46910 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726045AbgEAW5b (ORCPT ); Fri, 1 May 2020 18:57:31 -0400 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 47BA9206B8; Fri, 1 May 2020 22:57:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588373850; bh=LXBvB44SCeNdj+HATb89++1mLFiPdFO5sDwPGdqjuAU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=DlknOgeXeqcbZa1OyVRl65XfKUT1u5FqObkKr7/qhywD2d/0whjATnUElZ1L4S3ay +aRbeywfmDA2mpCO3qyD9rztfbyGP0dZB99vFMkOddoW9KKqwu+U3J8KEuSAA1BvXS 4NeZ9sLPOreeHinYU9kNjCYPmlkQLlDDJrJ6aqQM= Date: Fri, 1 May 2020 15:57:29 -0700 From: Andrew Morton To: Henry Willard Cc: , , Mel Gorman Subject: Re: [PATCH] mm: Limit boost_watermark on small zones. Message-Id: <20200501155729.a479c4b27f127d9aa866bd8e@linux-foundation.org> In-Reply-To: <1588294148-6586-1-git-send-email-henry.willard@oracle.com> References: <1588294148-6586-1-git-send-email-henry.willard@oracle.com> 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2400,6 +2400,14 @@ static inline void boost_watermark(struct zone *zone) > > if (!watermark_boost_factor) > return; > + /* > + * Don't bother in zones that are unlikely to produce results. > + * On small machines, including kdump capture kernels running > + * in a small area, boosting the watermark can cause an out of > + * memory situation immediately. > + */ > + if ((pageblock_nr_pages * 4) > zone_managed_pages(zone)) > + return; > > max_boost = mult_frac(zone->_watermark[WMARK_HIGH], > watermark_boost_factor, 10000); > -- > 1.8.3.1