Re: [stable] [PATCH 0/3] Reduce watermark-related problems withthe per-cpu allocator V4

[Greg KH]

On Tue, Sep 21, 2010 at 03:23:09PM +0100, Mel Gorman wrote:
> On Tue, Sep 21, 2010 at 05:58:14AM -0700, Greg KH wrote:
> > On Tue, Sep 21, 2010 at 12:17:41PM +0100, Mel Gorman wrote:
> > > On Fri, Sep 03, 2010 at 04:05:51PM -0700, Andrew Morton wrote:
> > > > On Fri,  3 Sep 2010 10:08:43 +0100
> > > > Mel Gorman <mel@xxxxxxxxx> 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@xxxxxxxxxx)
> > > > 
> > > > >  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.
> > > > 
> > > 
> > > These patches have made it to mainline as the following commits.
> > > 
> > > 9ee493c mm: page allocator: drain per-cpu lists after direct reclaim allocation fails
> > > aa45484 mm: page allocator: calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake
> > > 72853e2 mm: page allocator: update free page counters after pages are placed on the free list
> > > 
> > > I have not heard from the -stable guys, is there a reasonable
> > > expectation that they'll be picked up?
> > 
> > If you ask me, then I'll know to give a response :)
> > 
> 
> Hi Greg,
> 
> I would ask you directly but I didn't want anyone else on stable@ to
> feel left out :)
> 
> > None of these were tagged as going to the stable tree, should I include
> > them? 
> 
> Yes please unless there is a late objection. The patches were first developed
> as a result of a distro bug whose kernel was based on 2.6.32.  There was
> every indication this affected mainline as well. The details of the testing
> are above.
> 
> Dave Chinner had also reported problems with livelocks in reclaim that
> looked like IPI storms. There were two major factors at play and these
> patches addressed one of them. It works out as both a bug and a
> performance fix.
> 
> > If so, for which -stable tree?  .27, .32, and .35 are all
> > currently active.
> > 
> 
> 2.6.35 for certain.
> 
> I would have a strong preference for 2.6.32 as well as it's a baseline for
> a number of distros. The second commit will conflict with per-cpu changes
> but the resolution is straight-forward.

Thanks for the backport, I've queued these up for .32 and .35 now.

greg k-h
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