Re: sandy bridge kswapd0 livelock with pagecache

[Mel Gorman <mgorman@suse.de>]

On Fri, Jun 24, 2011 at 02:10:30PM +0100, P?draig Brady wrote:
> On 24/06/11 12:44, Mel Gorman wrote:
> > On Thu, Jun 23, 2011 at 08:25:40PM +0100, P?draig Brady wrote:
> >> On 23/06/11 17:59, Mel Gorman wrote:
> >>> On Thu, Jun 23, 2011 at 04:32:27PM +0100, P?draig Brady wrote:
> >>>> On 23/06/11 16:24, Mel Gorman wrote:
> >>>>>
> >>>>> Theory 2 it is then. This is to be applied on top of the patch for
> >>>>> theory 1.
> >>>>>
> >>>>> ==== CUT HERE ====
> >>>>> mm: vmscan: Prevent kswapd doing excessive work when classzone is unreclaimable
> >>>>
> >>>> No joy :(
> >>>>
> >>>
> >>> Joy is indeed rapidly fleeing the vicinity.
> >>>
> >>> Check /proc/sys/vm/laptop_mode . If it's set, unset it and try again.
> >>
> >> It was not set
> >>
> >>>
> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >>> index dce95dd..c8c0f5a 100644
> >>> --- a/mm/vmscan.c
> >>> +++ b/mm/vmscan.c
> >>> @@ -2426,19 +2426,19 @@ loop_again:
> >>>  			 * zone has way too many pages free already.
> >>>  			 */
> >>>  			if (!zone_watermark_ok_safe(zone, order,
> >>> -					8*high_wmark_pages(zone), end_zone, 0))
> >>
> >> Note 8 was not in my tree.
> >> Manually applied patch makes no difference :(
> >> Well maybe kswapd0 started spinning a little later.
> >>
> > 
> > Gack :)
> > 
> > On further reflection "mm: vmscan: Prevent kswapd doing excessive
> > work when classzone is unreclaimable" was off but it was along the
> > right lines in that the balancing classzone was not being considered
> > when going to sleep.
> > 
> > The following is a patch against mainline 2.6.38.8 and is a
> > roll-up of four separate patches that includes a new modification to
> > sleeping_prematurely. Because the stack I am working off has changed
> > significantly, it's far easier if you apply this on top of a vanilla
> > fedora branch of 2.6.38 and test rather than trying to backout and
> > reapply. Depending on when you checked out or if you have applied the
> > BALANCE_GAP patch yourself, it might collide with 8*high_wmark_pages
> > but the resolution should be straight-forward.
> > 
> > Thanks for persisting.
> 
> Bingo!

Sweet. Thanks for sticking with it. A rebase on top of 3.0-rc4 is in
the works. I'll ask for it to be merged for 2.6.38-stable where I'll
hopefully meet the window so that it gets picked up by Fedora.

-- 
Mel Gorman
SUSE Labs

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