On Tue, Mar 07, 2017 at 05:26:43PM +0300, Kirill A. Shutemov wrote: > On Thu, Mar 02, 2017 at 03:39:18PM +0900, Minchan Kim wrote: > > If the page is mapped and rescue in ttuo, page_mapcount(page) == 0 cannot > > be true so page_mapcount check in ttu is enough to return SWAP_SUCCESS. > > IOW, SWAP_MLOCK check is redundant so remove it. > > > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > --- > > mm/rmap.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > index 3a14013..0a48958 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -1523,7 +1523,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags) > > else > > ret = rmap_walk(page, &rwc); > > > > - if (ret != SWAP_MLOCK && !page_mapcount(page)) > > + if (!page_mapcount(page)) > > Hm. I think there's bug in current code. > It should be !total_mapcount(page) otherwise it can be false-positive if > there's THP mapped with PTEs. Hmm, I lost THP thesedays totally so I can miss something easily. When I look at that, it seems every pages passed try_to_unmap is already splited by split split_huge_page_to_list which calls freeze_page which split pmd. So I guess it's no problem. Right? Anyway, it's out of scope in this patch so if it's really problem, I'd like to handle it separately. One asking: When we should use total_mapcount instead of page_mapcount? If total_mapcount has some lengthy description, it would be very helpful for one who not is faimilar with that. > > And in this case ret != SWAP_MLOCK is helpful to cut down some cost. > Althouth it should be fine to remove it, I guess. Sure but be hard to measure it, I think. As well, later patch removes SWAP_MLOCK. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
