From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752990AbcGMIsK (ORCPT ); Wed, 13 Jul 2016 04:48:10 -0400 Received: from outbound-smtp11.blacknight.com ([46.22.139.16]:57113 "EHLO outbound-smtp11.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932230AbcGMIr4 (ORCPT ); Wed, 13 Jul 2016 04:47:56 -0400 Date: Wed, 13 Jul 2016 09:47:42 +0100 From: Mel Gorman To: Johannes Weiner Cc: Andrew Morton , Linux-MM , Rik van Riel , Vlastimil Babka , Minchan Kim , Joonsoo Kim , LKML Subject: Re: [PATCH 12/34] mm: vmscan: do not reclaim from kswapd if there is any eligible zone Message-ID: <20160713084742.GG9806@techsingularity.net> References: <1467970510-21195-1-git-send-email-mgorman@techsingularity.net> <1467970510-21195-13-git-send-email-mgorman@techsingularity.net> <20160712142909.GF5881@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20160712142909.GF5881@cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 12, 2016 at 10:29:09AM -0400, Johannes Weiner wrote: > > + /* > > + * If the number of buffer_heads in the machine exceeds the > > + * maximum allowed level then reclaim from all zones. This is > > + * not specific to highmem as highmem may not exist but it is > > + * it is expected that buffer_heads are stripped in writeback. > > The mention of highmem in this comment make only sense within the > context of this diff; it'll be pretty confusing in the standalone > code. > > Also, double "it is" :) Is this any better? Note that it's marked as a fix to a later patch to reduce collisions in mmotm. It's not a bisection risk so I saw little need to cause unnecessary conflicts for Andrew. ---8<--- mm, vmscan: Have kswapd reclaim from all zones if reclaiming and buffer_heads_over_limit -fix Johannes reported that the comment about buffer_heads_over_limit in balance_pgdat only made sense in the context of the patch. This patch clarifies the reasoning and how it applies to 32 and 64 bit systems. This is a fix to the mmotm patch mm-vmscan-have-kswapd-reclaim-from-all-zones-if-reclaiming-and-buffer_heads_over_limit.patch Suggested-by: Johannes Weiner Signed-off-by: Mel Gorman diff --git a/mm/vmscan.c b/mm/vmscan.c index d079210d46ee..21eae17ee730 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3131,12 +3131,13 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx) /* * If the number of buffer_heads exceeds the maximum allowed - * then consider reclaiming from all zones. This is not - * specific to highmem which may not exist but it is it is - * expected that buffer_heads are stripped in writeback. - * Reclaim may still not go ahead if all eligible zones - * for the original allocation request are balanced to - * avoid excessive reclaim from kswapd. + * then consider reclaiming from all zones. This has a dual + * purpose -- on 64-bit systems it is expected that + * buffer_heads are stripped during active rotation. On 32-bit + * systems, highmem pages can pin lowmem memory and shrinking + * buffers can relieve lowmem pressure. Reclaim may still not + * go ahead if all eligible zones for the original allocation + * request are balanced to avoid excessive reclaim from kswapd. */ if (buffer_heads_over_limit) { for (i = MAX_NR_ZONES - 1; i >= 0; i--) {