Yang Shi <yang....@linux.alibaba.com> writes: > On 5/9/19 7:12 PM, Huang, Ying wrote: >> Yang Shi <yang....@linux.alibaba.com> writes: >> >>> Since commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after >>> swapped out"), THP can be swapped out in a whole. But, nr_reclaimed >>> still gets inc'ed by one even though a whole THP (512 pages) gets >>> swapped out. >>> >>> This doesn't make too much sense to memory reclaim. For example, direct >>> reclaim may just need reclaim SWAP_CLUSTER_MAX pages, reclaiming one THP >>> could fulfill it. But, if nr_reclaimed is not increased correctly, >>> direct reclaim may just waste time to reclaim more pages, >>> SWAP_CLUSTER_MAX * 512 pages in worst case. >>> >>> This change may result in more reclaimed pages than scanned pages showed >>> by /proc/vmstat since scanning one head page would reclaim 512 base pages. >>> >>> Cc: "Huang, Ying" <ying.hu...@intel.com> >>> Cc: Johannes Weiner <han...@cmpxchg.org> >>> Cc: Michal Hocko <mho...@suse.com> >>> Cc: Mel Gorman <mgor...@techsingularity.net> >>> Cc: "Kirill A . Shutemov" <kirill.shute...@linux.intel.com> >>> Cc: Hugh Dickins <hu...@google.com> >>> Signed-off-by: Yang Shi <yang....@linux.alibaba.com> >>> --- >>> I'm not quite sure if it was the intended behavior or just omission. I tried >>> to dig into the review history, but didn't find any clue. I may miss some >>> discussion. >>> >>> mm/vmscan.c | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index fd9de50..7e026ec 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -1446,7 +1446,11 @@ static unsigned long shrink_page_list(struct >>> list_head *page_list, >>> unlock_page(page); >>> free_it: >>> - nr_reclaimed++; >>> + /* >>> + * THP may get swapped out in a whole, need account >>> + * all base pages. >>> + */ >>> + nr_reclaimed += (1 << compound_order(page)); >>> /* >>> * Is there need to periodically free_page_list? It would >> Good catch! Thanks! >> >> How about to change this to >> >> >> nr_reclaimed += hpage_nr_pages(page); > > Either is fine to me. Is this faster than "1 << compound_order(page)"?
I think the readability is a little better. And this will become nr_reclaimed += 1 if CONFIG_TRANSPARENT_HUAGEPAGE is disabled. Best Regards, Huang, Ying >> >> Best Regards, >> Huang, Ying