From b8f593cd0896b8b14c2b494a9776531b5cd54d98 Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Thu, 6 Jul 2017 15:37:28 -0700 Subject: mm, THP, swap: check whether THP can be split firstly To swap out THP (Transparent Huage Page), before splitting the THP, the swap cluster will be allocated and the THP will be added into the swap cache. But it is possible that the THP cannot be split, so that we must delete the THP from the swap cache and free the swap cluster. To avoid that, in this patch, whether the THP can be split is checked firstly. The check can only be done racy, but it is good enough for most cases. With the patch, the swap out throughput improves 3.6% (from about 4.16GB/s to about 4.31GB/s) in the vm-scalability swap-w-seq test case with 8 processes. The test is done on a Xeon E5 v3 system. The swap device used is a RAM simulated PMEM (persistent memory) device. To test the sequential swapping out, the test case creates 8 processes, which sequentially allocate and write to the anonymous pages until the RAM and part of the swap device is used up. Link: http://lkml.kernel.org/r/20170515112522.32457-5-ying.huang@intel.com Signed-off-by: "Huang, Ying" Acked-by: Kirill A. Shutemov [for can_split_huge_page()] Cc: Johannes Weiner Cc: Andrea Arcangeli Cc: Ebru Akagunduz Cc: Hugh Dickins Cc: Michal Hocko Cc: Minchan Kim Cc: Rik van Riel Cc: Shaohua Li Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'mm/vmscan.c') diff --git a/mm/vmscan.c b/mm/vmscan.c index 729e37f02de6..abaf0215a352 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1125,6 +1125,10 @@ static unsigned long shrink_page_list(struct list_head *page_list, !PageSwapCache(page)) { if (!(sc->gfp_mask & __GFP_IO)) goto keep_locked; + /* cannot split THP, skip it */ + if (PageTransHuge(page) && + !can_split_huge_page(page, NULL)) + goto activate_locked; if (!add_to_swap(page)) { if (!PageTransHuge(page)) goto activate_locked; -- cgit v1.2.3