Re: [PATCH v3] mm: thp: Set the accessed flag for old pages on accessfault.
From: Ni zhan Chen
Date: Fri Oct 26 2012 - 02:20:03 EST
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 <cmetcalf@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
---
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;
--
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