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? Thanks -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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>