Re: [PATCH 2/2] mm, thp: clear PG_mlocked when last mapping gone

[Vlastimil Babka <vbabka@suse.cz>]

On 12/29/2015 09:46 PM, Kirill A. Shutemov wrote:
> I missed clear_page_mlock() in page_remove_anon_compound_rmap().
> It usually shouldn't cause any problems since we munlock pages
> explicitly, but in conjunction with missed munlock in __oom_reap_vmas()
> it causes problems:
>   http://lkml.kernel.org/r/5661FBB6.6050307@oracle.com
>
> Let's put it in place an mirror behaviour for small pages.
>
> NOTE: I'm not entirely sure why we ever need clear_page_mlock() in
> page_remove_rmap() codepath. It looks redundant to me as we munlock
> pages anyway. But this is out of scope of the patch.

Git blame actually quickly points to commit e6c509f854550 which explains 
it :)

>
> The patch can be folded into
>   "thp: allow mlocked THP again"
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Ack.

> Reported-by: Sasha Levin <sasha.levin@oracle.com>
> ---
>   mm/rmap.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 384516fb7495..68af2e32f7ed 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1356,6 +1356,9 @@ static void page_remove_anon_compound_rmap(struct page *page)
>   		nr = HPAGE_PMD_NR;
>   	}
>
> +	if (unlikely(PageMlocked(page)))
> +		clear_page_mlock(page);
> +
>   	if (nr) {
>   		__mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr);
>   		deferred_split_huge_page(page);
>

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