Hi Vlastimil,
Thanks for comment!
On 2017/5/25 14:32, Vlastimil Babka wrote:
> On 05/25/2017 04:13 AM, Yisheng Xie wrote:
>> Kefeng reported that when run the follow test the mlock count
>
>> in meminfo
>> cannot be decreased:
>
> "increases permanently."?
Yes if I am not mis-understanding what your means.
>
>> [1] testcase
>> linux:~ # cat test_mlockal
>> grep Mlocked /proc/meminfo
>> for j in `seq 0 10`
>> do
>> for i in `seq 4 15`
>> do
>> ./p_mlockall >> log &
>> done
>> sleep 0.2
>> done
>> # wait some time to let mlock counter decrease and 5s may not enough
>> sleep 5
>> grep Mlocked /proc/meminfo
>>
>> linux:~ # cat p_mlockall.c
>> #include <sys/mman.h>
>> #include <stdlib.h>
>> #include <stdio.h>
>>
>> #define SPACE_LEN 4096
>>
>> int main(int argc, char ** argv)
>> {
>> int ret;
>> void *adr = malloc(SPACE_LEN);
>> if (!adr)
>> return -1;
>>
>> ret = mlockall(MCL_CURRENT | MCL_FUTURE);
>> printf("mlcokall ret = %d\n", ret);
>>
>> ret = munlockall();
>> printf("munlcokall ret = %d\n", ret);
>>
>> free(adr);
>> return 0;
>> }
>>
>> When __munlock_pagevec, we ClearPageMlock but isolation_failed in race
>> condition, and we do not count these page into delta_munlocked, which cause
>> mlock counter incorrect for we had Clear the PageMlock and cannot count down
>> the number in the feture.
>
> Can I suggest the following instead:
>
> In __munlock_pagevec() we should decrement NR_MLOCK for each page where
> we clear the PageMlocked flag. Commit 1ebb7cc6a583 ("mm: munlock: batch
> NR_MLOCK zone state updates") has introduced a bug where we don't
> decrement NR_MLOCK for pages where we clear the flag, but fail to
> isolate them from the lru list (e.g. when the pages are on some other
> cpu's percpu pagevec). Since PageMlocked stays cleared, the NR_MLOCK
> accounting gets permanently disrupted by this.
That's much better and clear. Should I send another version ?
Thanks
Yisheng Xie
>
>> Fix it by count the number of page whoes PageMlock flag is cleared.
>>
>> Fixes: 1ebb7cc6a583 (" mm: munlock: batch NR_MLOCK zone state updates")
>> Signed-off-by: Yisheng Xie <[email protected]>
>> Reported-by: Kefeng Wang <[email protected]>
>> Tested-by: Kefeng Wang <[email protected]>
>> Cc: Vlastimil Babka <[email protected]>
>
> Acked-by: Vlastimil Babka <[email protected]>
>
> Thanks!
>
>> Cc: Joern Engel <[email protected]>
>> Cc: Mel Gorman <[email protected]>
>> Cc: Michel Lespinasse <[email protected]>
>> Cc: Hugh Dickins <[email protected]>
>> Cc: Rik van Riel <[email protected]>
>> Cc: Johannes Weiner <[email protected]>
>> Cc: Michal Hocko <[email protected]>
>> Cc: Xishi Qiu <[email protected]>
>> CC: zhongjiang <[email protected]>
>> Cc: Hanjun Guo <[email protected]>
>> Cc: <[email protected]>
>> ---
>> v2:
>> - use delta_munlocked for it doesn't do the increment in fastpath -
>> Vlastimil
>>
>> Hi Andrew:
>> Could you please help to fold this?
>>
>> Thanks
>> Yisheng Xie
>>
>> mm/mlock.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/mlock.c b/mm/mlock.c
>> index c483c5c..b562b55 100644
>> --- a/mm/mlock.c
>> +++ b/mm/mlock.c
>> @@ -284,7 +284,7 @@ static void __munlock_pagevec(struct pagevec *pvec,
>> struct zone *zone)
>> {
>> int i;
>> int nr = pagevec_count(pvec);
>> - int delta_munlocked;
>> + int delta_munlocked = -nr;
>> struct pagevec pvec_putback;
>> int pgrescued = 0;
>>
>> @@ -304,6 +304,8 @@ static void __munlock_pagevec(struct pagevec *pvec,
>> struct zone *zone)
>> continue;
>> else
>> __munlock_isolation_failed(page);
>> + } else {
>> + delta_munlocked++;
>> }
>>
>> /*
>> @@ -315,7 +317,6 @@ static void __munlock_pagevec(struct pagevec *pvec,
>> struct zone *zone)
>> pagevec_add(&pvec_putback, pvec->pages[i]);
>> pvec->pages[i] = NULL;
>> }
>> - delta_munlocked = -nr + pagevec_count(&pvec_putback);
>> __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
>> spin_unlock_irq(zone_lru_lock(zone));
>>
>>
>
>
> .
>
