linux-kernel - Re: [PATCH] mm: Do not walk all of system memory during show

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 31 Oct 2013 00:55:40 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	kosaki.motohiro@...il.com, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Do not walk all of system memory during show_mem

(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@...e.de>

That's ok. I haven't used such information on my long oom debugging history.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/