The patch titled
Subject: thp: fix huge zero page logic for page with pfn == 0
has been added to the -mm tree. Its filename is
thp-fix-huge-zero-page-logic-for-page-with-pfn-==-0.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: thp: fix huge zero page logic for page with pfn == 0
Current implementation of huge zero page uses pfn value 0 to indicate that
the page hasn't allocated yet. It assumes that buddy page allocator can't
return page with pfn == 0.
Let's rework the code to store 'struct page *' of huge zero page, not its
pfn. This way we can avoid the weak assumption.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 43 +++++++++++++++++++++----------------------
1 file changed, 21 insertions(+), 22 deletions(-)
diff -puN mm/huge_memory.c~thp-fix-huge-zero-page-logic-for-page-with-pfn-==-0 mm/huge_memory.c
--- a/mm/huge_memory.c~thp-fix-huge-zero-page-logic-for-page-with-pfn-==-0
+++ a/mm/huge_memory.c
@@ -163,25 +163,24 @@ static int start_khugepaged(void)
}
static atomic_t huge_zero_refcount;
-static unsigned long huge_zero_pfn __read_mostly;
+static struct page *huge_zero_page __read_mostly;
-static inline bool is_huge_zero_pfn(unsigned long pfn)
+static inline bool is_huge_zero_page(struct page *page)
{
- unsigned long zero_pfn = ACCESS_ONCE(huge_zero_pfn);
- return zero_pfn && pfn == zero_pfn;
+ return ACCESS_ONCE(huge_zero_page) == page;
}
static inline bool is_huge_zero_pmd(pmd_t pmd)
{
- return is_huge_zero_pfn(pmd_pfn(pmd));
+ return is_huge_zero_page(pmd_page(pmd));
}
-static unsigned long get_huge_zero_page(void)
+static struct page *get_huge_zero_page(void)
{
struct page *zero_page;
retry:
if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
- return ACCESS_ONCE(huge_zero_pfn);
+ return ACCESS_ONCE(huge_zero_page);
zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
HPAGE_PMD_ORDER);
@@ -191,7 +190,7 @@ retry:
}
count_vm_event(THP_ZERO_PAGE_ALLOC);
preempt_disable();
- if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
+ if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
preempt_enable();
__free_page(zero_page);
goto retry;
@@ -200,7 +199,7 @@ retry:
/* We take additional reference here. It will be put back by shrinker */
atomic_set(&huge_zero_refcount, 2);
preempt_enable();
- return ACCESS_ONCE(huge_zero_pfn);
+ return ACCESS_ONCE(huge_zero_page);
}
static void put_huge_zero_page(void)
@@ -220,9 +219,9 @@ static int shrink_huge_zero_page(struct
return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
- unsigned long zero_pfn = xchg(&huge_zero_pfn, 0);
- BUG_ON(zero_pfn == 0);
- __free_page(__pfn_to_page(zero_pfn));
+ struct page *zero_page = xchg(&huge_zero_page, NULL);
+ BUG_ON(zero_page == NULL);
+ __free_page(zero_page);
}
return 0;
@@ -764,12 +763,12 @@ static inline struct page *alloc_hugepag
static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
- unsigned long zero_pfn)
+ struct page *zero_page)
{
pmd_t entry;
if (!pmd_none(*pmd))
return false;
- entry = pfn_pmd(zero_pfn, vma->vm_page_prot);
+ entry = mk_pmd(zero_page, vma->vm_page_prot);
entry = pmd_wrprotect(entry);
entry = pmd_mkhuge(entry);
set_pmd_at(mm, haddr, pmd, entry);
@@ -794,20 +793,20 @@ int do_huge_pmd_anonymous_page(struct mm
if (!(flags & FAULT_FLAG_WRITE) &&
transparent_hugepage_use_zero_page()) {
pgtable_t pgtable;
- unsigned long zero_pfn;
+ struct page *zero_page;
bool set;
pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable))
return VM_FAULT_OOM;
- zero_pfn = get_huge_zero_page();
- if (unlikely(!zero_pfn)) {
+ zero_page = get_huge_zero_page();
+ if (unlikely(!zero_page)) {
pte_free(mm, pgtable);
count_vm_event(THP_FAULT_FALLBACK);
goto out;
}
spin_lock(&mm->page_table_lock);
set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
- zero_pfn);
+ zero_page);
spin_unlock(&mm->page_table_lock);
if (!set) {
pte_free(mm, pgtable);
@@ -886,16 +885,16 @@ int copy_huge_pmd(struct mm_struct *dst_
* a page table.
*/
if (is_huge_zero_pmd(pmd)) {
- unsigned long zero_pfn;
+ struct page *zero_page;
bool set;
/*
* get_huge_zero_page() will never allocate a new page here,
* since we already have a zero page to copy. It just takes a
* reference.
*/
- zero_pfn = get_huge_zero_page();
+ zero_page = get_huge_zero_page();
set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
- zero_pfn);
+ zero_page);
BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
ret = 0;
goto out_unlock;
@@ -1812,7 +1811,7 @@ int split_huge_page_to_list(struct page
struct anon_vma *anon_vma;
int ret = 1;
- BUG_ON(is_huge_zero_pfn(page_to_pfn(page)));
+ BUG_ON(is_huge_zero_page(page));
BUG_ON(!PageAnon(page));
/*
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
thp-fix-huge-zero-page-logic-for-page-with-pfn-==-0.patch
--
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