On Tue, Jan 05, 2016 at 10:37:18AM +0100, Vlastimil Babka wrote: > 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@xxxxxxxxxx > > > >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 > :) Okay, it explains situation somewhat. The thing which still makes me a bit uncomfortable with the situation is that we remove PG_mlocked only when the last mapping of the page gone. It's not necessary the mapping which was VM_LOCKED. It means we can rely on the clear_page_mlock() inside page_remove_rmap() only when remove all page mappings at once (like in truncate case). The clear_page_mlock() also helps hide real mlock leak bugs, like fixed by patch 1/2: we saliently munlock page when last mapping gone, even if the VMA was never been mlocked in the first place. That's kinda suboptimal. > > > > >The patch can be folded into > > "thp: allow mlocked THP again" > > > >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > Ack. > > >Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > >--- > > 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); > > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>