On 9/16/19 12:36 PM, Michal Hocko wrote:
> On Fri 13-09-19 12:18:49, Kirill A. Shutemov wrote:
>> Adding fully unmapped pages into deferred split queue is not productive:
>> these pages are about to be freed or they are pinned and cannot be split
>> anyway.
>>
>> Signed-off-by: Kirill A. Shutemov <[email protected]>
>> ---
>> mm/rmap.c | 14 ++++++++++----
>> 1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 003377e24232..45388f1bf317 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct
>> page *page)
>> if (TestClearPageDoubleMap(page)) {
>> /*
>> * Subpages can be mapped with PTEs too. Check how many of
>> - * themi are still mapped.
>> + * them are still mapped.
>> */
>> for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
>> if (atomic_add_negative(-1, &page[i]._mapcount))
>> nr++;
>> }
>> +
>> + /*
>> + * Queue the page for deferred split if at least one small
>> + * page of the compound page is unmapped, but at least one
>> + * small page is still mapped.
>> + */
>> + if (nr && nr < HPAGE_PMD_NR)
>> + deferred_split_huge_page(page);
>
> You've set nr to zero in the for loop so this cannot work AFAICS.
The for loop then does nr++ for each subpage that's still mapped?
>> } else {
>> nr = HPAGE_PMD_NR;
>> }
>> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct
>> page *page)
>> if (unlikely(PageMlocked(page)))
>> clear_page_mlock(page);
>>
>> - if (nr) {
>> + if (nr)
>> __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
>> - deferred_split_huge_page(page);
>> - }
>> }
>>
>> /**
>> --
>> 2.21.0
>
