The patch titled
Subject: mm: numa: do not trap faults on the huge zero page
has been added to the -mm tree. Its filename is
mm-numa-do-not-trap-faults-on-the-huge-zero-page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-numa-do-not-trap-faults-on-the-huge-zero-page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-numa-do-not-trap-faults-on-the-huge-zero-page.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxx>
Subject: mm: numa: do not trap faults on the huge zero page
Faults on the huge zero page are pointless and there is a BUG_ON to catch
them during fault time. This patch reintroduces a check that avoids
marking the zero page PAGE_NONE.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kirill Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/huge_mm.h | 3 ++-
mm/huge_memory.c | 13 ++++++++++++-
mm/memory.c | 1 -
mm/mprotect.c | 14 +++++++++++++-
4 files changed, 27 insertions(+), 4 deletions(-)
diff -puN include/linux/huge_mm.h~mm-numa-do-not-trap-faults-on-the-huge-zero-page include/linux/huge_mm.h
--- a/include/linux/huge_mm.h~mm-numa-do-not-trap-faults-on-the-huge-zero-page
+++ a/include/linux/huge_mm.h
@@ -31,7 +31,8 @@ extern int move_huge_pmd(struct vm_area_
unsigned long new_addr, unsigned long old_end,
pmd_t *old_pmd, pmd_t *new_pmd);
extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
- unsigned long addr, pgprot_t newprot);
+ unsigned long addr, pgprot_t newprot,
+ int prot_numa);
enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_FLAG,
diff -puN mm/huge_memory.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page mm/huge_memory.c
--- a/mm/huge_memory.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page
+++ a/mm/huge_memory.c
@@ -1497,7 +1497,7 @@ out:
* - HPAGE_PMD_NR is protections changed and TLB flush necessary
*/
int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
- unsigned long addr, pgprot_t newprot)
+ unsigned long addr, pgprot_t newprot, int prot_numa)
{
struct mm_struct *mm = vma->vm_mm;
spinlock_t *ptl;
@@ -1505,6 +1505,17 @@ int change_huge_pmd(struct vm_area_struc
if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
pmd_t entry;
+
+ /*
+ * Avoid trapping faults against the zero page. The read-only
+ * data is likely to be read-cached on the local CPU and
+ * local/remote hits to the zero page are not interesting.
+ */
+ if (prot_numa && is_huge_zero_pmd(*pmd)) {
+ spin_unlock(ptl);
+ return 0;
+ }
+
ret = 1;
entry = pmdp_get_and_clear_notify(mm, addr, pmd);
entry = pmd_modify(entry, newprot);
diff -puN mm/memory.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page mm/memory.c
--- a/mm/memory.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page
+++ a/mm/memory.c
@@ -3037,7 +3037,6 @@ static int do_numa_page(struct mm_struct
pte_unmap_unlock(ptep, ptl);
return 0;
}
- BUG_ON(is_zero_pfn(page_to_pfn(page)));
/*
* Avoid grouping on DSO/COW pages in specific and RO pages
diff -puN mm/mprotect.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page mm/mprotect.c
--- a/mm/mprotect.c~mm-numa-do-not-trap-faults-on-the-huge-zero-page
+++ a/mm/mprotect.c
@@ -76,6 +76,18 @@ static unsigned long change_pte_range(st
if (pte_present(oldpte)) {
pte_t ptent;
+ /*
+ * Avoid trapping faults against the zero or KSM
+ * pages. See similar comment in change_huge_pmd.
+ */
+ if (prot_numa) {
+ struct page *page;
+
+ page = vm_normal_page(vma, addr, oldpte);
+ if (!page || PageKsm(page))
+ continue;
+ }
+
ptent = ptep_modify_prot_start(mm, addr, pte);
ptent = pte_modify(ptent, newprot);
@@ -142,7 +154,7 @@ static inline unsigned long change_pmd_r
split_huge_page_pmd(vma, addr, pmd);
else {
int nr_ptes = change_huge_pmd(vma, pmd, addr,
- newprot);
+ newprot, prot_numa);
if (nr_ptes) {
if (nr_ptes == HPAGE_PMD_NR) {
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
mm-debug-pagealloc-prepare-boottime-configurable-on-off.patch
mm-vmscan-prevent-kswapd-livelock-due-to-pfmemalloc-throttled-process-being-killed.patch
mm-page_alloc-place-zone_id-check-before-vm_bug_on_page-check.patch
mm-vmscan-wake-up-all-pfmemalloc-throttled-processes-at-once.patch
mm-numa-do-not-dereference-pmd-outside-of-the-lock-during-numa-hinting-fault.patch
mm-add-p-protnone-helpers-for-use-by-numa-balancing.patch
mm-convert-p_numa-users-to-p_protnone_numa.patch
ppc64-add-paranoid-warnings-for-unexpected-dsisr_protfault.patch
mm-convert-p_mknonnuma-and-remaining-page-table-manipulations.patch
mm-remove-remaining-references-to-numa-hinting-bits-and-helpers.patch
mm-numa-do-not-trap-faults-on-the-huge-zero-page.patch
x86-mm-restore-original-pte_special-check.patch
mm-numa-add-paranoid-check-around-pte_protnone_numa.patch
mm-numa-avoid-unnecessary-tlb-flushes-when-setting-numa-hinting-entries.patch
do_shared_fault-check-that-mmap_sem-is-held.patch
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