On 2017/5/26 17:06, Vlastimil Babka wrote:
> On 05/26/2017 05:54 AM, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@xxxxxxxxxx>
>>
>> Recently, when I address in the issue, Subject "mlock: fix mlock count
>> can not decrease in race condition" had been take over, I review
>> the code and find the potential issue. it will result in the incorrect
>> account, it will make us misunderstand straightforward.
>>
>> The following testcase can prove the issue.
>>
>> int main(void)
>> {
>> char *map;
>> int fd;
>>
>> fd = open("test", O_CREAT|O_RDWR);
>> unlink("test");
>> ftruncate(fd, 4096);
>> map = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE, fd, 0);
>> map[0] = 11;
>> mlock(map, 4096);
>> ftruncate(fd, 0);
>> close(fd);
>> munlock(map, 4096);
>> munmap(map, 4096);
>>
>> return 0;
>> }
>>
>> before:
>> unevictable_pgs_mlocked 10589
>> unevictable_pgs_munlocked 10588
>> unevictable_pgs_cleared 1
>>
>> apply the patch;
>> after:
>> unevictable_pgs_mlocked 9497
>> unevictable_pgs_munlocked 9497
>> unevictable_pgs_cleared 1
>>
>> unmap_mapping_range unmap them, page_remove_rmap will deal with
>> clear_page_mlock situation. we clear page Mlock flag and successful
>> isolate the page, the page will putback the evictable list. but it is not
>> record the munlock event.
>>
>> The patch add the event account when successful page isolation.
>>
>> Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
> Hi,
>
> I think this is by design. UNEVICTABLE_PGMUNLOCKED is supposed for explicit
> munlock() actions from userspace. Truncation etc is counted by
> UNEVICTABLE_PGCLEARED.
>
> Vlastimil
it seems make sense. but the we just mmap the specified ragne and mlock it.
when the process drop out, exit_mmap will call munlock_vma_pages_all to
unmap the mlock range and make the event normal.
Do you think?
Thanks
zhongjinag
>> ---
>> mm/mlock.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/mlock.c b/mm/mlock.c
>> index c483c5c..941930b 100644
>> --- a/mm/mlock.c
>> +++ b/mm/mlock.c
>> @@ -64,6 +64,7 @@ void clear_page_mlock(struct page *page)
>> -hpage_nr_pages(page));
>> count_vm_event(UNEVICTABLE_PGCLEARED);
>> if (!isolate_lru_page(page)) {
>> + count_vm_event(UNEVICTABLE_PGMUNLOCKED);
>> putback_lru_page(page);
>> } else {
>> /*
>>
>
> .
>
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