From 8f182270dfec432e93fae14f9208a6b9af01009f Mon Sep 17 00:00:00 2001 From: Lukasz Odzioba Date: Fri, 24 Jun 2016 14:50:01 -0700 Subject: [PATCH] mm/swap.c: flush lru pvecs on compound page arrival Currently we can have compound pages held on per cpu pagevecs, which leads to a lot of memory unavailable for reclaim when needed. In the systems with hundreads of processors it can be GBs of memory. On of the way of reproducing the problem is to not call munmap explicitly on all mapped regions (i.e. after receiving SIGTERM). After that some pages (with THP enabled also huge pages) may end up on lru_add_pvec, example below. void main() { #pragma omp parallel { size_t size = 55 * 1000 * 1000; // smaller than MEM/CPUS void *p = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS , -1, 0); if (p != MAP_FAILED) memset(p, 0, size); //munmap(p, size); // uncomment to make the problem go away } } When we run it with THP enabled it will leave significant amount of memory on lru_add_pvec. This memory will be not reclaimed if we hit OOM, so when we run above program in a loop: for i in `seq 100`; do ./a.out; done many processes (95% in my case) will be killed by OOM. The primary point of the LRU add cache is to save the zone lru_lock contention with a hope that more pages will belong to the same zone and so their addition can be batched. The huge page is already a form of batched addition (it will add 512 worth of memory in one go) so skipping the batching seems like a safer option when compared to a potential excess in the caching which can be quite large and much harder to fix because lru_add_drain_all is way to expensive and it is not really clear what would be a good moment to call it. Similarly we can reproduce the problem on lru_deactivate_pvec by adding: madvise(p, size, MADV_FREE); after memset. This patch flushes lru pvecs on compound page arrival making the problem less severe - after applying it kill rate of above example drops to 0%, due to reducing maximum amount of memory held on pvec from 28MB (with THP) to 56kB per CPU. Suggested-by: Michal Hocko Link: http://lkml.kernel.org/r/1466180198-18854-1-git-send-email-lukasz.odzioba@intel.com Signed-off-by: Lukasz Odzioba Acked-by: Michal Hocko Cc: Kirill Shutemov Cc: Andrea Arcangeli Cc: Vladimir Davydov Cc: Ming Li Cc: Minchan Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/mm/swap.c b/mm/swap.c index 59f5faf..90530ff 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -242,7 +242,7 @@ void rotate_reclaimable_page(struct page *page) get_page(page); local_irq_save(flags); pvec = this_cpu_ptr(&lru_rotate_pvecs); - if (!pagevec_add(pvec, page)) + if (!pagevec_add(pvec, page) || PageCompound(page)) pagevec_move_tail(pvec); local_irq_restore(flags); } @@ -296,7 +296,7 @@ void activate_page(struct page *page) struct pagevec *pvec = &get_cpu_var(activate_page_pvecs); get_page(page); - if (!pagevec_add(pvec, page)) + if (!pagevec_add(pvec, page) || PageCompound(page)) pagevec_lru_move_fn(pvec, __activate_page, NULL); put_cpu_var(activate_page_pvecs); } @@ -391,9 +391,8 @@ static void __lru_cache_add(struct page *page) struct pagevec *pvec = &get_cpu_var(lru_add_pvec); get_page(page); - if (!pagevec_space(pvec)) + if (!pagevec_add(pvec, page) || PageCompound(page)) __pagevec_lru_add(pvec); - pagevec_add(pvec, page); put_cpu_var(lru_add_pvec); } @@ -628,7 +627,7 @@ void deactivate_file_page(struct page *page) if (likely(get_page_unless_zero(page))) { struct pagevec *pvec = &get_cpu_var(lru_deactivate_file_pvecs); - if (!pagevec_add(pvec, page)) + if (!pagevec_add(pvec, page) || PageCompound(page)) pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL); put_cpu_var(lru_deactivate_file_pvecs); } @@ -648,7 +647,7 @@ void deactivate_page(struct page *page) struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs); get_page(page); - if (!pagevec_add(pvec, page)) + if (!pagevec_add(pvec, page) || PageCompound(page)) pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL); put_cpu_var(lru_deactivate_pvecs); } -- 2.7.4