linux-kernel - Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu allocator V4

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]

Message-Id: <20100903160551.05db4a92.akpm@linux-foundation.org>
Date:	Fri, 3 Sep 2010 16:05:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	stable@...nel.org, Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 0/3] Reduce watermark-related problems with the per-cpu
 allocator V4

On Fri,  3 Sep 2010 10:08:43 +0100
Mel Gorman <mel@....ul.ie> wrote:

> The noteworthy change is to patch 2 which now uses the generic
> zone_page_state_snapshot() in zone_nr_free_pages(). Similar logic still
> applies for *when* zone_page_state_snapshot() to avoid ovedhead.
> 
> Changelog since V3
>   o Use generic helper for NR_FREE_PAGES estimate when necessary
> 
> Changelog since V2
>   o Minor clarifications
>   o Rebase to 2.6.36-rc3
> 
> Changelog since V1
>   o Fix for !CONFIG_SMP
>   o Correct spelling mistakes
>   o Clarify a ChangeLog
>   o Only check for counter drift on machines large enough for the counter
>     drift to breach the min watermark when NR_FREE_PAGES report the low
>     watermark is fine
> 
> Internal IBM test teams beta testing distribution kernels have reported
> problems on machines with a large number of CPUs whereby page allocator
> failure messages show huge differences between the nr_free_pages vmstat
> counter and what is available on the buddy lists. In an extreme example,
> nr_free_pages was above the min watermark but zero pages were on the buddy
> lists allowing the system to potentially livelock unable to make forward
> progress unless an allocation succeeds. There is no reason why the problems
> would not affect mainline so the following series mitigates the problems
> in the page allocator related to to per-cpu counter drift and lists.
> 
> The first patch ensures that counters are updated after pages are added to
> free lists.
> 
> The second patch notes that the counter drift between nr_free_pages and what
> is on the per-cpu lists can be very high. When memory is low and kswapd
> is awake, the per-cpu counters are checked as well as reading the value
> of NR_FREE_PAGES. This will slow the page allocator when memory is low and
> kswapd is awake but it will be much harder to breach the min watermark and
> potentially livelock the system.
> 
> The third patch notes that after direct-reclaim an allocation can
> fail because the necessary pages are on the per-cpu lists. After a
> direct-reclaim-and-allocation-failure, the per-cpu lists are drained and
> a second attempt is made.
> 
> Performance tests against 2.6.36-rc3 did not show up anything interesting. A
> version of this series that continually called vmstat_update() when
> memory was low was tested internally and found to help the counter drift
> problem. I described this during LSF/MM Summit and the potential for IPI
> storms was frowned upon. An alternative fix is in patch two which uses
> for_each_online_cpu() to read the vmstat deltas while memory is low and
> kswapd is awake. This should be functionally similar.
> 
> This patch should be merged after the patch "vmstat : update
> zone stat threshold at onlining a cpu" which is in mmotm as
> vmstat-update-zone-stat-threshold-when-onlining-a-cpu.patch .
> 
> If we can agree on it, this series is a stable candidate.

(cc stable@...nel.org)

>  include/linux/mmzone.h |   13 +++++++++++++
>  include/linux/vmstat.h |   22 ++++++++++++++++++++++
>  mm/mmzone.c            |   21 +++++++++++++++++++++
>  mm/page_alloc.c        |   29 +++++++++++++++++++++--------
>  mm/vmstat.c            |   15 ++++++++++++++-
>  5 files changed, 91 insertions(+), 9 deletions(-)

For the entire patch series I get

 include/linux/mmzone.h |   13 +++++++++++++
 include/linux/vmstat.h |   22 ++++++++++++++++++++++
 mm/mmzone.c            |   21 +++++++++++++++++++++
 mm/page_alloc.c        |   33 +++++++++++++++++++++++----------
 mm/vmstat.c            |   16 +++++++++++++++-
 5 files changed, 94 insertions(+), 11 deletions(-)

The patches do apply OK to 2.6.35.

Give the extent and the coreness of it all, it's a bit more than I'd
usually push at the -stable guys.  But I guess that if the patches fix
all the issues you've noted, as well as David's "minute-long livelocks
in memory reclaim" then yup, it's worth backporting it all.



--
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/