From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 58D166B0005 for ; Tue, 12 Jul 2016 10:05:14 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id f126so14370575wma.3 for ; Tue, 12 Jul 2016 07:05:14 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id c127si20756226wmd.112.2016.07.12.07.05.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Jul 2016 07:05:13 -0700 (PDT) Date: Tue, 12 Jul 2016 10:05:04 -0400 From: Johannes Weiner Subject: Re: [PATCH 06/34] mm, vmscan: have kswapd only scan based on the highest requested zone Message-ID: <20160712140504.GC5881@cmpxchg.org> References: <1467970510-21195-1-git-send-email-mgorman@techsingularity.net> <1467970510-21195-7-git-send-email-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1467970510-21195-7-git-send-email-mgorman@techsingularity.net> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Linux-MM , Rik van Riel , Vlastimil Babka , Minchan Kim , Joonsoo Kim , LKML On Fri, Jul 08, 2016 at 10:34:42AM +0100, Mel Gorman wrote: > kswapd checks all eligible zones to see if they need balancing even if it > was woken for a lower zone. This made sense when we reclaimed on a > per-zone basis because we wanted to shrink zones fairly so avoid > age-inversion problems. Ideally this is completely unnecessary when > reclaiming on a per-node basis. In theory, there may still be anomalies > when all requests are for lower zones and very old pages are preserved in > higher zones but this should be the exceptional case. > > Signed-off-by: Mel Gorman > Acked-by: Vlastimil Babka Acked-by: Johannes Weiner I wasn't quite sure at first what the rationale is for this patch, since it probably won't make much difference in pratice. But I do agree that the code is cleaner to have kswapd check exactly what it was asked to check, rather than some do-the-"right"-thing magic. A hypothetical onslaught of low-zone allocations will wreak havoc to the page age in higher zones anyway, right? So I don't think that case matters all that much. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org