Johannes Weiner <han...@cmpxchg.org> writes: > On Wed, Apr 19, 2017 at 03:06:25PM +0800, Huang, Ying wrote: >> From: Huang Ying <ying.hu...@intel.com> >> >> 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. >> >> Cc: Johannes Weiner <han...@cmpxchg.org> >> Signed-off-by: "Huang, Ying" <ying.hu...@intel.com> >> --- >> mm/swap_state.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/mm/swap_state.c b/mm/swap_state.c >> index 3a3217f68937..b025c9878e5e 100644 >> --- a/mm/swap_state.c >> +++ b/mm/swap_state.c >> @@ -192,9 +192,15 @@ int add_to_swap(struct page *page, struct list_head >> *list) >> VM_BUG_ON_PAGE(!PageLocked(page), page); >> VM_BUG_ON_PAGE(!PageUptodate(page), page); >> >> - /* cannot split, skip it */ >> - if (unlikely(PageTransHuge(page)) && !can_split_huge_page(page, NULL)) >> - return 0; >> + if (unlikely(PageTransHuge(page))) { >> + /* cannot split, skip it */ >> + if (!can_split_huge_page(page, NULL)) >> + return 0; >> + /* fallback to split huge page firstly if no PMD map */ >> + if (!compound_mapcount(page) && >> + split_huge_page_to_list(page, list)) >> + return 0; >> + } > > This looks good to me, but could you please elaborate the comment a > little bit with what you have in the changelog? Something like: > > /* > * Split pages without a PMD map right away. Chances are > * some or all of the tail pages can be freed without IO. > */
The comments look much better! Thanks! I will change it. Best Regards, Huang, Ying