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
> ---
> 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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