On Fri, Oct 26, 2012 at 10:07:15AM +0100, Will Deacon wrote: > On Fri, Oct 26, 2012 at 08:44:35AM +0100, Kirill A. Shutemov wrote: > > On Thu, Oct 25, 2012 at 05:44:31PM +0100, Will Deacon wrote: > > > On x86 memory accesses to pages without the ACCESSED flag set result in > > > the > > > ACCESSED flag being set automatically. With the ARM architecture a page > > > access > > > fault is raised instead (and it will continue to be raised until the > > > ACCESSED > > > flag is set for the appropriate PTE/PMD). > > > > > > For normal memory pages, handle_pte_fault will call pte_mkyoung > > > (effectively > > > setting the ACCESSED flag). For transparent huge pages, pmd_mkyoung will > > > only > > > be called for a write fault. > > > > > > This patch ensures that faults on transparent hugepages which do not > > > result > > > in a CoW update the access flags for the faulting pmd. > > > > > > Cc: Chris Metcalf <cmetc...@tilera.com> > > > Cc: Kirill A. Shutemov <kir...@shutemov.name> > > > Cc: Andrea Arcangeli <aarca...@redhat.com> > > > Signed-off-by: Will Deacon <will.dea...@arm.com> > > > --- > > > > > > Ok chaps, I rebased this thing onto today's next (which basically > > > necessitated a rewrite) so I've reluctantly dropped my acks and kindly > > > ask if you could eyeball the new code, especially where the locking is > > > concerned. In the numa code (do_huge_pmd_prot_none), Peter checks again > > > that the page is not splitting, but I can't see why that is required. > > > > In handle_mm_fault() we check if the pmd is under splitting without > > page_table_lock. It's kind of speculative cheap check. We need to re-check > > if the PMD is really not under splitting after taking page_table_lock. > > I appreciate the need to check whether the thing is splitting, but I thought > that the pmd_same(*pmd, orig_pmd) check after taking the page_table_lock > would be sufficient, because we know that the entry hasn't changed and that > it wasn't splitting before we took the lock. This also mirrors the approach > taken by do_huge_pmd_wp_page. > > Is there something I'm missing?
Hm.. You're correct from my POV. Acked-by: Kirill A. Shutemov <kir...@shutemov.name> I think the check in do_huge_pmd_prot_none() is redundant. It only add latency. I'll prepare patch to remove it. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
