From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx108.postini.com [74.125.245.108]) by kanga.kvack.org (Postfix) with SMTP id CB5C76B0072 for ; Fri, 26 Oct 2012 02:20:07 -0400 (EDT) Received: by mail-ia0-f169.google.com with SMTP id h37so2463390iak.14 for ; Thu, 25 Oct 2012 23:20:07 -0700 (PDT) Message-ID: <508A2B8B.7020608@gmail.com> Date: Fri, 26 Oct 2012 14:19:55 +0800 From: Ni zhan Chen MIME-Version: 1.0 Subject: Re: [PATCH v3] mm: thp: Set the accessed flag for old pages on access fault. References: <1351183471-14710-1-git-send-email-will.deacon@arm.com> In-Reply-To: <1351183471-14710-1-git-send-email-will.deacon@arm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Will Deacon Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mhocko@suse.cz, peterz@infradead.org, akpm@linux-foundation.org, Chris Metcalf , "Kirill A. Shutemov" , Andrea Arcangeli On 10/26/2012 12:44 AM, 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. Could you write changlog? > > Cc: Chris Metcalf > Cc: Kirill A. Shutemov > Cc: Andrea Arcangeli > Signed-off-by: Will Deacon > --- > > 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. > > Cheers, > > Will Could you explain why you not call pmd_trans_huge_lock to confirm the pmd is splitting or stable as Andrea point out? > > include/linux/huge_mm.h | 4 ++++ > mm/huge_memory.c | 22 ++++++++++++++++++++++ > mm/memory.c | 7 ++++++- > 3 files changed, 32 insertions(+), 1 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 4f0f948..766fb27 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -8,6 +8,10 @@ extern int do_huge_pmd_anonymous_page(struct mm_struct *mm, > extern int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr, > struct vm_area_struct *vma); > +extern void huge_pmd_set_accessed(struct mm_struct *mm, > + struct vm_area_struct *vma, > + unsigned long address, pmd_t *pmd, > + pmd_t orig_pmd, int dirty); > extern int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, > unsigned long address, pmd_t *pmd, > pmd_t orig_pmd); > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 3c14a96..f024d98 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -932,6 +932,28 @@ out: > return ret; > } > > +void huge_pmd_set_accessed(struct mm_struct *mm, > + struct vm_area_struct *vma, > + unsigned long address, > + pmd_t *pmd, pmd_t orig_pmd, > + int dirty) > +{ > + pmd_t entry; > + unsigned long haddr; > + > + spin_lock(&mm->page_table_lock); > + if (unlikely(!pmd_same(*pmd, orig_pmd))) > + goto unlock; > + > + entry = pmd_mkyoung(orig_pmd); > + haddr = address & HPAGE_PMD_MASK; > + if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty)) > + update_mmu_cache_pmd(vma, address, pmd); > + > +unlock: > + spin_unlock(&mm->page_table_lock); > +} > + > static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm, > struct vm_area_struct *vma, > unsigned long address, > diff --git a/mm/memory.c b/mm/memory.c > index f21ac1c..bcbc084 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3650,12 +3650,14 @@ retry: > > barrier(); > if (pmd_trans_huge(orig_pmd) && !pmd_trans_splitting(orig_pmd)) { > + unsigned int dirty = flags & FAULT_FLAG_WRITE; > + > if (pmd_numa(vma, orig_pmd)) { > do_huge_pmd_numa_page(mm, vma, address, pmd, > flags, orig_pmd); > } > > - if ((flags & FAULT_FLAG_WRITE) && !pmd_write(orig_pmd)) { > + if (dirty && !pmd_write(orig_pmd)) { > ret = do_huge_pmd_wp_page(mm, vma, address, pmd, > orig_pmd); > /* > @@ -3665,6 +3667,9 @@ retry: > */ > if (unlikely(ret & VM_FAULT_OOM)) > goto retry; > + } else { > + huge_pmd_set_accessed(mm, vma, address, pmd, > + orig_pmd, dirty); > } > > return ret; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org