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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>