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thp: fix huge zero page logic for page with pfn == 0

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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.

[akpm@linux-foundation.org: fix sparse warning]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Minchan Kim <minchan@kernel.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2013-04-29 15:08:44 -07:00 committed by Linus Torvalds
parent fd0ccaf2bd
commit 5918d10a4b
1 changed files with 22 additions and 23 deletions
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45
mm/huge_memory.c
View File

@ -163,35 +163,34 @@ static int start_khugepaged(void)
} }
static atomic_t huge_zero_refcount; 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 ACCESS_ONCE(huge_zero_page) == page;
return zero_pfn && pfn == zero_pfn;
} }
static inline bool is_huge_zero_pmd(pmd_t pmd) 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; struct page *zero_page;
retry: retry:
if (likely(atomic_inc_not_zero(&huge_zero_refcount))) 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, zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
HPAGE_PMD_ORDER); HPAGE_PMD_ORDER);
if (!zero_page) { if (!zero_page) {
count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED); count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
return 0; return NULL;
} }
count_vm_event(THP_ZERO_PAGE_ALLOC); count_vm_event(THP_ZERO_PAGE_ALLOC);
preempt_disable(); preempt_disable();
if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) { if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
preempt_enable(); preempt_enable();
__free_page(zero_page); __free_page(zero_page);
goto retry; goto retry;
@ -200,7 +199,7 @@ retry:
/* We take additional reference here. It will be put back by shrinker */ /* We take additional reference here. It will be put back by shrinker */
atomic_set(&huge_zero_refcount, 2); atomic_set(&huge_zero_refcount, 2);
preempt_enable(); preempt_enable();
return ACCESS_ONCE(huge_zero_pfn); return ACCESS_ONCE(huge_zero_page);
} }
static void put_huge_zero_page(void) static void put_huge_zero_page(void)
@ -220,9 +219,9 @@ static int shrink_huge_zero_page(struct shrinker *shrink,
return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0; return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) { if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
unsigned long zero_pfn = xchg(&huge_zero_pfn, 0); struct page *zero_page = xchg(&huge_zero_page, NULL);
BUG_ON(zero_pfn == 0); BUG_ON(zero_page == NULL);
__free_page(__pfn_to_page(zero_pfn)); __free_page(zero_page);
} }
return 0; return 0;
@ -764,12 +763,12 @@ static inline struct page *alloc_hugepage(int defrag)
static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm, static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd, struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
unsigned long zero_pfn) struct page *zero_page)
{ {
pmd_t entry; pmd_t entry;
if (!pmd_none(*pmd)) if (!pmd_none(*pmd))
return false; 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_wrprotect(entry);
entry = pmd_mkhuge(entry); entry = pmd_mkhuge(entry);
set_pmd_at(mm, haddr, pmd, entry); set_pmd_at(mm, haddr, pmd, entry);
@ -794,20 +793,20 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (!(flags & FAULT_FLAG_WRITE) && if (!(flags & FAULT_FLAG_WRITE) &&
transparent_hugepage_use_zero_page()) { transparent_hugepage_use_zero_page()) {
pgtable_t pgtable; pgtable_t pgtable;
unsigned long zero_pfn; struct page *zero_page;
bool set; bool set;
pgtable = pte_alloc_one(mm, haddr); pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable)) if (unlikely(!pgtable))
return VM_FAULT_OOM; return VM_FAULT_OOM;
zero_pfn = get_huge_zero_page(); zero_page = get_huge_zero_page();
if (unlikely(!zero_pfn)) { if (unlikely(!zero_page)) {
pte_free(mm, pgtable); pte_free(mm, pgtable);
count_vm_event(THP_FAULT_FALLBACK); count_vm_event(THP_FAULT_FALLBACK);
goto out; goto out;
} }
spin_lock(&mm->page_table_lock); spin_lock(&mm->page_table_lock);
set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd, set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
zero_pfn); zero_page);
spin_unlock(&mm->page_table_lock); spin_unlock(&mm->page_table_lock);
if (!set) { if (!set) {
pte_free(mm, pgtable); pte_free(mm, pgtable);
@ -886,16 +885,16 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* a page table. * a page table.
*/ */
if (is_huge_zero_pmd(pmd)) { if (is_huge_zero_pmd(pmd)) {
unsigned long zero_pfn; struct page *zero_page;
bool set; bool set;
/* /*
* get_huge_zero_page() will never allocate a new page here, * get_huge_zero_page() will never allocate a new page here,
* since we already have a zero page to copy. It just takes a * since we already have a zero page to copy. It just takes a
* reference. * 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, set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
zero_pfn); zero_page);
BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */ BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
ret = 0; ret = 0;
goto out_unlock; goto out_unlock;
@ -1812,7 +1811,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
struct anon_vma *anon_vma; struct anon_vma *anon_vma;
int ret = 1; int ret = 1;
BUG_ON(is_huge_zero_pfn(page_to_pfn(page))); BUG_ON(is_huge_zero_page(page));
BUG_ON(!PageAnon(page)); BUG_ON(!PageAnon(page));
/* /*