On 20.11.18 14:43, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > filemap_map_pages takes a speculative reference to each page in the > range before it tries to lock that page. While this is correct it > also can influence page migration which will bail out when seeing > an elevated reference count. The faultaround code would bail on > seeing a locked page so we can pro-actively check the PageLocked > bit before page_cache_get_speculative and prevent from pointless > reference count churn. > > Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> > Suggested-by: Jan Kara <jack@xxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/filemap.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 81adec8ee02c..c76d6a251770 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2553,6 +2553,9 @@ void filemap_map_pages(struct vm_fault *vmf, > goto next; > > head = compound_head(page); > + > + if (PageLocked(head)) > + goto next; > if (!page_cache_get_speculative(head)) > goto next; > > Right, no sense in referencing a page if we know we will drop the reference right away. Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
