From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
To: Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>
Cc: kosaki.motohiro@gmail.com, Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: Do not walk all of system memory during show_mem
Date: Thu, 31 Oct 2013 00:55:40 -0400 [thread overview]
Message-ID: <5271E2CC.8040702@gmail.com> (raw)
In-Reply-To: <20131016104228.GM11028@suse.de>
(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 <mgorman@suse.de>
That's ok. I haven't used such information on my long oom debugging history.
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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prev parent reply other threads:[~2013-10-31 4:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-16 10:42 [PATCH] mm: Do not walk all of system memory during show_mem Mel Gorman
2013-10-17 1:11 ` David Rientjes
2013-11-04 10:08 ` Mel Gorman
2013-12-03 14:57 ` [PATCH] mm, show_mem: Remove SHOW_MEM_FILTER_PAGE_COUNT Mel Gorman
2013-12-03 23:41 ` David Rientjes
2013-10-31 4:55 ` KOSAKI Motohiro [this message]
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