Messages in this thread | | | From | Mel Gorman <> | Subject | [PATCH 0/4] [RFC] Functional fix to zone_reclaim() and bring behaviour more in line with expectations V2 | Date | Tue, 9 Jun 2009 18:01:40 +0100 |
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Changelog since V1 o Rebase to mmotm o Add various acks o Documentation and patch leader fixes o Use Kosaki's method for calculating the number of unmapped pages o Consider the zone full in more situations than all pages being unreclaimable o Add a counter to detect when scan-avoidance heuristics are failing o Handle jiffie wraps for zone_reclaim_interval o Move zone_reclaim_interval to the end of the set with the view to dropping it. If Kosaki's calculation is accurate, then the problem being dealt with should also be addressed
A bug was brought to my attention against a distro kernel but it affects mainline and I believe problems like this have been reported in various guises on the mailing lists although I don't have specific examples at the moment.
The problem is that malloc() stalled for a long time (minutes in some cases) if a large tmpfs mount was occupying a large percentage of memory overall. The pages did not get cleaned or reclaimed by zone_reclaim() because the zone_reclaim_mode was unsuitable, but the lists are uselessly scanned frequencly making the CPU spin at near 100%.
This patchset intends to address that bug and bring the behaviour of zone_reclaim() more in line with expectations. It is based on top of mmotm and takes advantage of Kosaki's work with respect to zone_reclaim().
Patch 1 alters the heuristics that zone_reclaim() uses to determine if the scan should go ahead. Currently, it is basically assuming zone_reclaim_mode is 1 and historically it could not deal with tmpfs pages at all. This fixes up the heuristic so that the scan is more likely to be correctly avoided.
Patch 2 notes that zone_reclaim() returning a failure automatically means the zone is marked full. This is not always true. It could have failed because the GFP mask or zone_reclaim_mode were unsuitable.
Patch 3 introduces a counter zreclaim_failed that will increment each time the zone_reclaim scan-avoidance heuristics fail. If that counter is rapidly increasing, then zone_reclaim_mode should be set to 0 as a temporarily resolution and a bug reported.
Patch 4 reintroduces zone_reclaim_interval to catch the situation where zone_reclaim() cannot tell in advance that the scan is a waste of time. This is a brute force catch-all. I've asked the bug reporter to test with just patch 1. If that works, then this patch will be dropped and patch 3 will be enough to tell us if/when the situation occured again. Even with this patch applied, the counter will increase slowly so it's still possible to detect the problem.
Documentation/sysctl/vm.txt | 15 +++++++ include/linux/mmzone.h | 9 ++++ include/linux/swap.h | 1 + include/linux/vmstat.h | 3 + kernel/sysctl.c | 9 ++++ mm/internal.h | 4 ++ mm/page_alloc.c | 26 ++++++++++-- mm/vmscan.c | 91 ++++++++++++++++++++++++++++++++++--------- mm/vmstat.c | 3 + 9 files changed, 138 insertions(+), 23 deletions(-)
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