From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752484Ab3JaEzq (ORCPT ); Thu, 31 Oct 2013 00:55:46 -0400 Received: from mail-qa0-f43.google.com ([209.85.216.43]:58289 "EHLO mail-qa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752212Ab3JaEzo (ORCPT ); Thu, 31 Oct 2013 00:55:44 -0400 Message-ID: <5271E2CC.8040702@gmail.com> Date: Thu, 31 Oct 2013 00:55:40 -0400 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Mel Gorman , Andrew Morton CC: kosaki.motohiro@gmail.com, Linux-MM , LKML Subject: Re: [PATCH] mm: Do not walk all of system memory during show_mem References: <20131016104228.GM11028@suse.de> In-Reply-To: <20131016104228.GM11028@suse.de> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (10/16/13 6:42 AM), Mel Gorman wrote: > It has been reported on very large machines that show_mem is taking almost > 5 minutes to display information. This is a serious problem if there is > an OOM storm. The bulk of the cost is in show_mem doing a very expensive > PFN walk to give us the following information > > Total RAM: Also available as totalram_pages > Highmem pages: Also available as totalhigh_pages > Reserved pages: Can be inferred from the zone structure > Shared pages: PFN walk required > Unshared pages: PFN walk required > Quick pages: Per-cpu walk required > > Only the shared/unshared pages requires a full PFN walk but that information > is useless. It is also inaccurate as page pins of unshared pages would > be accounted for as shared. Even if the information was accurate, I'm > struggling to think how the shared/unshared information could be useful > for debugging OOM conditions. Maybe it was useful before rmap existed when > reclaiming shared pages was costly but it is less relevant today. > > The PFN walk could be optimised a bit but why bother as the information is > useless. This patch deletes the PFN walker and infers the total RAM, highmem > and reserved pages count from struct zone. It omits the shared/unshared page > usage on the grounds that it is useless. It also corrects the reporting > of HighMem as HighMem/MovableOnly as ZONE_MOVABLE has similar problems to > HighMem with respect to lowmem/highmem exhaustion. > > Signed-off-by: Mel Gorman That's ok. I haven't used such information on my long oom debugging history. Acked-by: KOSAKI Motohiro