On Fri, May 15, 2015 at 11:15:00AM +0200, Vlastimil Babka wrote: > On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote: > >With new refcounting we will be able map the same compound page with > >PTEs and PMDs. It requires adjustment to conditions when we can reuse > >the page on write-protection fault. > > > >For PTE fault we can't reuse the page if it's part of huge page. > > > >For PMD we can only reuse the page if nobody else maps the huge page or > >it's part. We can do it by checking page_mapcount() on each sub-page, > >but it's expensive. > > > >The cheaper way is to check page_count() to be equal 1: every mapcount > >takes page reference, so this way we can guarantee, that the PMD is the > >only mapping. > > > >This approach can give false negative if somebody pinned the page, but > >that doesn't affect correctness. > > > >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > >Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > > So couldn't the same trick be used in Patch 1 to avoid counting individual > oder-0 pages? Hm. You're right, we could. But is smaps that performance sensitive to bother? -- 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>