From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f178.google.com (mail-ie0-f178.google.com [209.85.223.178]) by kanga.kvack.org (Postfix) with ESMTP id 1BE8A6B0035 for ; Thu, 31 Oct 2013 00:55:50 -0400 (EDT) Received: by mail-ie0-f178.google.com with SMTP id x13so4149007ief.9 for ; Wed, 30 Oct 2013 21:55:49 -0700 (PDT) Received: from psmtp.com ([74.125.245.119]) by mx.google.com with SMTP id b10si1501855icq.131.2013.10.30.21.55.46 for ; Wed, 30 Oct 2013 21:55:48 -0700 (PDT) Received: by mail-qa0-f46.google.com with SMTP id j15so4276935qaq.19 for ; Wed, 30 Oct 2013 21:55:44 -0700 (PDT) Message-ID: <5271E2CC.8040702@gmail.com> Date: Thu, 31 Oct 2013 00:55:40 -0400 From: KOSAKI Motohiro MIME-Version: 1.0 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: owner-linux-mm@kvack.org List-ID: To: Mel Gorman , Andrew Morton Cc: kosaki.motohiro@gmail.com, Linux-MM , LKML (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 -- 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