Commit 747552b1 authored Jul 06, 2017 by Huang Ying Committed by Linus Torvalds Jul 06, 2017

mm, THP, swap: enable THP swap optimization only if has compound map

If there is no compound map for a THP (Transparent Huge Page), it is
possible that the map count of some sub-pages of the THP is 0.  So it is
better to split the THP before swapping out.  In this way, the sub-pages
not mapped will be freed, and we can avoid the unnecessary swap out
operations for these sub-pages.

Link: http://lkml.kernel.org/r/20170515112522.32457-6-ying.huang@intel.com


Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b8f593cd

mm/vmscan.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -1125,10 +1125,19 @@ static unsigned long shrink_page_list(struct list_head *page_list,
		!PageSwapCache(page)) {
		if (!(sc->gfp_mask & __GFP_IO))
		goto keep_locked;
		if (PageTransHuge(page)) {
		/* cannot split THP, skip it */
		if (PageTransHuge(page) &&
		!can_split_huge_page(page, NULL))
		if (!can_split_huge_page(page, NULL))
		goto activate_locked;
		/*
		* Split pages without a PMD map right
		* away. Chances are some or all of the
		* tail pages can be freed without IO.
		*/
		if (!compound_mapcount(page) &&
		split_huge_page_to_list(page, page_list))
		goto activate_locked;
		}
		if (!add_to_swap(page)) {
		if (!PageTransHuge(page))
		goto activate_locked;

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