On Tue, Nov 20, 2018 at 03:12:07PM +0100, Michal Hocko wrote: > On Tue 20-11-18 17:07:15, Kirill A. Shutemov wrote: > > On Tue, Nov 20, 2018 at 02:43:23PM +0100, 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. > > > > Looks fine to me. > > Thanks for the review. > > > But please drop a line of comment in the code. As is it might be confusing > > for a reader. > > This? Yep. Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > diff --git a/mm/filemap.c b/mm/filemap.c > index c76d6a251770..7c4e439a2e85 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2554,6 +2554,10 @@ void filemap_map_pages(struct vm_fault *vmf, > > head = compound_head(page); > > + /* > + * Check the locked pages before taking a reference to not > + * go in the way of migration. > + */ > if (PageLocked(head)) > goto next; > if (!page_cache_get_speculative(head)) > -- > Michal Hocko > SUSE Labs -- Kirill A. Shutemov
