[PATCH v3 04/10] thp: do_huge_pmd_wp_page(): handle huge zero page

From: Kirill A. Shutemov
Date: Tue Oct 02 2012 - 11:21:22 EST

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

On right access to huge zero page we alloc a new page and clear it.

In fallback path we create a new table and set pte around fault address
to the newly allocated page. All other ptes set to normal zero page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
include/linux/mm.h | 8 ++++
mm/huge_memory.c | 102 ++++++++++++++++++++++++++++++++++++++++++++--------
mm/memory.c | 7 ----
3 files changed, 95 insertions(+), 22 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 311be90..179a41c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -514,6 +514,14 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
}
#endif

+#ifndef my_zero_pfn
+static inline unsigned long my_zero_pfn(unsigned long addr)
+{
+ extern unsigned long zero_pfn;
+ return zero_pfn;
+}
+#endif
+
/*
* Multiple processes may "see" the same page. E.g. for untouched
* mappings of /dev/null, all processes see the same page full of
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c8b157d..f30f39d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -868,6 +868,61 @@ pgtable_t get_pmd_huge_pte(struct mm_struct *mm)
return pgtable;
}

+static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
+ struct vm_area_struct *vma, unsigned long address,
+ pmd_t *pmd, unsigned long haddr)
+{
+ pgtable_t pgtable;
+ pmd_t _pmd;
+ struct page *page;
+ int i, ret = 0;
+
+ page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+ if (!page) {
+ ret |= VM_FAULT_OOM;
+ goto out;
+ }
+
+ if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
+ put_page(page);
+ ret |= VM_FAULT_OOM;
+ goto out;
+ }
+
+ clear_user_highpage(page, address);
+ __SetPageUptodate(page);
+
+ spin_lock(&mm->page_table_lock);
+ pmdp_clear_flush_notify(vma, haddr, pmd);
+ /* leave pmd empty until pte is filled */
+
+ pgtable = get_pmd_huge_pte(mm);
+ pmd_populate(mm, &_pmd, pgtable);
+
+ for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+ pte_t *pte, entry;
+ if (haddr == (address & PAGE_MASK)) {
+ entry = mk_pte(page, vma->vm_page_prot);
+ entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+ page_add_new_anon_rmap(page, vma, haddr);
+ } else {
+ entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
+ entry = pte_mkspecial(entry);
+ }
+ pte = pte_offset_map(&_pmd, haddr);
+ VM_BUG_ON(!pte_none(*pte));
+ set_pte_at(mm, haddr, pte, entry);
+ pte_unmap(pte);
+ }
+ smp_wmb(); /* make pte visible before pmd */
+ pmd_populate(mm, pmd, pgtable);
+ spin_unlock(&mm->page_table_lock);
+
+ ret |= VM_FAULT_WRITE;
+out:
+ return ret;
+}
+
static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address,
@@ -965,17 +1020,19 @@ 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)
{
int ret = 0;
- struct page *page, *new_page;
+ struct page *page = NULL, *new_page;
unsigned long haddr;

VM_BUG_ON(!vma->anon_vma);
+ haddr = address & HPAGE_PMD_MASK;
+ if (is_huge_zero_pmd(orig_pmd))
+ goto alloc;
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(*pmd, orig_pmd)))
goto out_unlock;

page = pmd_page(orig_pmd);
VM_BUG_ON(!PageCompound(page) || !PageHead(page));
- haddr = address & HPAGE_PMD_MASK;
if (page_mapcount(page) == 1) {
pmd_t entry;
entry = pmd_mkyoung(orig_pmd);
@@ -987,7 +1044,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
}
get_page(page);
spin_unlock(&mm->page_table_lock);
-
+alloc:
if (transparent_hugepage_enabled(vma) &&
!transparent_hugepage_debug_cow())
new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
@@ -997,28 +1054,39 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,

if (unlikely(!new_page)) {
count_vm_event(THP_FAULT_FALLBACK);
- ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
- pmd, orig_pmd, page, haddr);
- if (ret & VM_FAULT_OOM)
- split_huge_page(page);
- put_page(page);
+ if (is_huge_zero_pmd(orig_pmd)) {
+ ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
+ address, pmd, haddr);
+ } else {
+ ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
+ pmd, orig_pmd, page, haddr);
+ if (ret & VM_FAULT_OOM)
+ split_huge_page(page);
+ put_page(page);
+ }
goto out;
}
count_vm_event(THP_FAULT_ALLOC);

if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
put_page(new_page);
- split_huge_page(page);
- put_page(page);
+ if (page) {
+ split_huge_page(page);
+ put_page(page);
+ }
ret |= VM_FAULT_OOM;
goto out;
}

- copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
+ if (is_huge_zero_pmd(orig_pmd))
+ clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
+ else
+ copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
__SetPageUptodate(new_page);

spin_lock(&mm->page_table_lock);
- put_page(page);
+ if (page)
+ put_page(page);
if (unlikely(!pmd_same(*pmd, orig_pmd))) {
spin_unlock(&mm->page_table_lock);
mem_cgroup_uncharge_page(new_page);
@@ -1026,7 +1094,6 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
goto out;
} else {
pmd_t entry;
- VM_BUG_ON(!PageHead(page));
entry = mk_pmd(new_page, vma->vm_page_prot);
entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
entry = pmd_mkhuge(entry);
@@ -1034,8 +1101,13 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
page_add_new_anon_rmap(new_page, vma, haddr);
set_pmd_at(mm, haddr, pmd, entry);
update_mmu_cache(vma, address, entry);
- page_remove_rmap(page);
- put_page(page);
+ if (is_huge_zero_pmd(orig_pmd))
+ add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ if (page) {
+ VM_BUG_ON(!PageHead(page));
+ page_remove_rmap(page);
+ put_page(page);
+ }
ret |= VM_FAULT_WRITE;
}
out_unlock:
diff --git a/mm/memory.c b/mm/memory.c
index 5736170..dbd92ba 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -724,13 +724,6 @@ static inline int is_zero_pfn(unsigned long pfn)
}
#endif

-#ifndef my_zero_pfn
-static inline unsigned long my_zero_pfn(unsigned long addr)
-{
- return zero_pfn;
-}
-#endif
-
/*
* vm_normal_page -- This function gets the "struct page" associated with a pte.
*
--
1.7.7.6

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