linux/mm, branch v3.0

vmscan: fix a livelock in kswapd

2011-07-20T05:09:31Z

I'm running a workload which triggers a lot of swap in a machine with 4 nodes. After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or kswapd2 are keeping running and I can't access filesystem, but most memory is free. This looks like a regression since commit 08951e545918c159 ("mm: vmscan: correct check for kswapd sleeping in sleeping_prematurely"). Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if all zones have watermark ok, end_zone will keep 0. Later sleeping_prematurely() always returns true. Because this is an order 3 wakeup, and if classzone_idx is 0, both balanced_pages and present_pages in pgdat_balanced() are 0. We add a special case here. If a zone has no page, we think it's balanced. This fixes the livelock. Signed-off-by: Shaohua Li Acked-by: Mel Gorman Cc: Minchan Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/nommu.c: fix remap_pfn_range()

2011-07-09T04:14:44Z

remap_pfn_range() means map physical address pfn<vm_start = pfn << PAGE_SHIFT which is wrong acroding the original meaning of this function. And some driver developer using remap_pfn_range() with correct parameter will get unexpected result because vm_start is changed. It should be implementd like addr = pfn << PAGE_SHIFT but which is meanless on nommu arch, this patch just make it simply return. Parameter name and setting of vma->vm_flags also be fixed. Signed-off-by: Bob Liu Cc: Geert Uytterhoeven Cc: David Howells Acked-by: Greg Ungerer Cc: Mike Frysinger Cc: Bob Liu Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

memcg: fix numa scan information update to be triggered by memory event

2011-07-09T04:14:44Z

commit 889976dbcb12 ("memcg: reclaim memory from nodes in round-robin order") adds an numa node round-robin for memcg. But the information is updated once per 10sec. This patch changes the update trigger from jiffies to memcg's event count. After this patch, numa scan information will be updated when we see 1024 events of pagein/pageout under a memcg. [akpm@linux-foundation.org: attempt to repair code layout] Signed-off-by: KAMEZAWA Hiroyuki Cc: Michal Hocko Cc: Ying Han Cc: Johannes Weiner Cc: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

memcg: fix reclaimable lru check in memcg

2011-07-09T04:14:43Z

Now, in mem_cgroup_hierarchical_reclaim(), mem_cgroup_local_usage() is used for checking whether the memcg contains reclaimable pages or not. If no pages in it, the routine skips it. But, mem_cgroup_local_usage() contains Unevictable pages and cannot handle "noswap" condition correctly. This doesn't work on a swapless system. This patch adds test_mem_cgroup_reclaimable() and replaces mem_cgroup_local_usage(). test_mem_cgroup_reclaimable() see LRU counter and returns correct answer to the caller. And this new function has "noswap" argument and can see only FILE LRU if necessary. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: fix kerneldoc layout] Signed-off-by: KAMEZAWA Hiroyuki Cc: Michal Hocko Cc: Ying Han Cc: Johannes Weiner Cc: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: __tlb_remove_page() check the correct batch

2011-07-09T04:14:43Z

__tlb_remove_page() switches to a new batch page, but still checks space in the old batch. This check always fails, and causes a forced tlb flush. Signed-off-by: Shaohua Li Acked-by: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: vmscan: only read new_classzone_idx from pgdat when reclaiming successfully

2011-07-09T04:14:43Z

During allocator-intensive workloads, kswapd will be woken frequently causing free memory to oscillate between the high and min watermark. This is expected behaviour. Unfortunately, if the highest zone is small, a problem occurs. When balance_pgdat() returns, it may be at a lower classzone_idx than it started because the highest zone was unreclaimable. Before checking if it should go to sleep though, it checks pgdat->classzone_idx which when there is no other activity will be MAX_NR_ZONES-1. It interprets this as it has been woken up while reclaiming, skips scheduling and reclaims again. As there is no useful reclaim work to do, it enters into a loop of shrinking slab consuming loads of CPU until the highest zone becomes reclaimable for a long period of time. There are two problems here. 1) If the returned classzone or order is lower, it'll continue reclaiming without scheduling. 2) if the highest zone was marked unreclaimable but balance_pgdat() returns immediately at DEF_PRIORITY, the new lower classzone is not communicated back to kswapd() for sleeping. This patch does two things that are related. If the end_zone is unreclaimable, this information is communicated back. Second, if the classzone or order was reduced due to failing to reclaim, new information is not read from pgdat and instead an attempt is made to go to sleep. Due to this, it is also necessary that pgdat->classzone_idx be initialised each time to pgdat->nr_zones - 1 to avoid re-reads being interpreted as wakeups. Signed-off-by: Mel Gorman Reported-by: Pádraig Brady Tested-by: Pádraig Brady Tested-by: Andrew Lutomirski Acked-by: Rik van Riel Cc: Minchan Kim Cc: KOSAKI Motohiro Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: vmscan: evaluate the watermarks against the correct classzone

2011-07-09T04:14:43Z

When deciding if kswapd is sleeping prematurely, the classzone is taken into account but this is different to what balance_pgdat() and the allocator are doing. Specifically, the DMA zone will be checked based on the classzone used when waking kswapd which could be for a GFP_KERNEL or GFP_HIGHMEM request. The lowmem reserve limit kicks in, the watermark is not met and kswapd thinks it's sleeping prematurely keeping kswapd awake in error. Signed-off-by: Mel Gorman Reported-by: Pádraig Brady Tested-by: Pádraig Brady Tested-by: Andrew Lutomirski Acked-by: Rik van Riel Reviewed-by: Minchan Kim Cc: KOSAKI Motohiro Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: vmscan: do not apply pressure to slab if we are not applying pressure to zone

2011-07-09T04:14:43Z

During allocator-intensive workloads, kswapd will be woken frequently causing free memory to oscillate between the high and min watermark. This is expected behaviour. When kswapd applies pressure to zones during node balancing, it checks if the zone is above a high+balance_gap threshold. If it is, it does not apply pressure but it unconditionally shrinks slab on a global basis which is excessive. In the event kswapd is being kept awake due to a high small unreclaimable zone, it skips zone shrinking but still calls shrink_slab(). Once pressure has been applied, the check for zone being unreclaimable is being made before the check is made if all_unreclaimable should be set. This miss of unreclaimable can cause has_under_min_watermark_zone to be set due to an unreclaimable zone preventing kswapd backing off on congestion_wait(). Signed-off-by: Mel Gorman Reported-by: Pádraig Brady Tested-by: Pádraig Brady Tested-by: Andrew Lutomirski Acked-by: Rik van Riel Reviewed-by: Minchan Kim Reviewed-by: KOSAKI Motohiro Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: vmscan: correct check for kswapd sleeping in sleeping_prematurely

2011-07-09T04:14:42Z

During allocator-intensive workloads, kswapd will be woken frequently causing free memory to oscillate between the high and min watermark. This is expected behaviour. Unfortunately, if the highest zone is small, a problem occurs. This seems to happen most with recent sandybridge laptops but it's probably a co-incidence as some of these laptops just happen to have a small Normal zone. The reproduction case is almost always during copying large files that kswapd pegs at 100% CPU until the file is deleted or cache is dropped. The problem is mostly down to sleeping_prematurely() keeping kswapd awake when the highest zone is small and unreclaimable and compounded by the fact we shrink slabs even when not shrinking zones causing a lot of time to be spent in shrinkers and a lot of memory to be reclaimed. Patch 1 corrects sleeping_prematurely to check the zones matching the classzone_idx instead of all zones. Patch 2 avoids shrinking slab when we are not shrinking a zone. Patch 3 notes that sleeping_prematurely is checking lower zones against a high classzone which is not what allocators or balance_pgdat() is doing leading to an artifical belief that kswapd should be still awake. Patch 4 notes that when balance_pgdat() gives up on a high zone that the decision is not communicated to sleeping_prematurely() This problem affects 2.6.38.8 for certain and is expected to affect 2.6.39 and 3.0-rc4 as well. If accepted, they need to go to -stable to be picked up by distros and this series is against 3.0-rc4. I've cc'd people that reported similar problems recently to see if they still suffer from the problem and if this fixes it. This patch: correct the check for kswapd sleeping in sleeping_prematurely() During allocator-intensive workloads, kswapd will be woken frequently causing free memory to oscillate between the high and min watermark. This is expected behaviour. A problem occurs if the highest zone is small. balance_pgdat() only considers unreclaimable zones when priority is DEF_PRIORITY but sleeping_prematurely considers all zones. It's possible for this sequence to occur 1. kswapd wakes up and enters balance_pgdat() 2. At DEF_PRIORITY, marks highest zone unreclaimable 3. At DEF_PRIORITY-1, ignores highest zone setting end_zone 4. At DEF_PRIORITY-1, calls shrink_slab freeing memory from highest zone, clearing all_unreclaimable. Highest zone is still unbalanced 5. kswapd returns and calls sleeping_prematurely 6. sleeping_prematurely looks at *all* zones, not just the ones being considered by balance_pgdat. The highest small zone has all_unreclaimable cleared but the zone is not balanced. all_zones_ok is false so kswapd stays awake This patch corrects the behaviour of sleeping_prematurely to check the zones balance_pgdat() checked. Signed-off-by: Mel Gorman Reported-by: Pádraig Brady Tested-by: Pádraig Brady Tested-by: Andrew Lutomirski Acked-by: Rik van Riel Reviewed-by: Minchan Kim Reviewed-by: KOSAKI Motohiro Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

memcg: fix direct softlimit reclaim to be called in limit path

2011-06-28T01:00:13Z

Commit d149e3b25d7c ("memcg: add the soft_limit reclaim in global direct reclaim") adds a softlimit hook to shrink_zones(). By this, soft limit is called as try_to_free_pages() do_try_to_free_pages() shrink_zones() mem_cgroup_soft_limit_reclaim() Then, direct reclaim is memcg softlimit hint aware, now. But, the memory cgroup's "limit" path can call softlimit shrinker. try_to_free_mem_cgroup_pages() do_try_to_free_pages() shrink_zones() mem_cgroup_soft_limit_reclaim() This will cause a global reclaim when a memcg hits limit. This is bug. soft_limit_reclaim() should be called when scanning_global_lru(sc) == true. And the commit adds a variable "total_scanned" for counting softlimit scanned pages....it's not "total". This patch removes the variable and update sc->nr_scanned instead of it. This will affect shrink_slab()'s scan condition but, global LRU is scanned by softlimit and I think this change makes sense. TODO: avoid too much scanning of a zone when softlimit did enough work. Signed-off-by: KAMEZAWA Hiroyuki Cc: Daisuke Nishimura Cc: Ying Han Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds