From: Huang Ying <ying.huang@xxxxxxxxx> Subject: 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@xxxxxxxxx Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Shaohua Li <shli@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff -puN mm/vmscan.c~mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map mm/vmscan.c --- a/mm/vmscan.c~mm-thp-swap-enable-thp-swap-optimization-only-if-has-compound-map +++ a/mm/vmscan.c @@ -1125,10 +1125,19 @@ static unsigned long shrink_page_list(st !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 (PageTransHuge(page)) { + /* cannot split THP, skip it */ + 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; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
