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thp: add compound_trans_head() helper

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Cleanup some code with common compound_trans_head helper.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2011-01-13 15:47:20 -08:00 committed by Linus Torvalds
parent 29ad768cfc
commit 22e5c47ee2
3 changed files with 35 additions and 36 deletions
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18
include/linux/huge_mm.h
View file

@ -126,6 +126,23 @@ static inline int hpage_nr_pages(struct page *page)
return HPAGE_PMD_NR;
return 1;
}
static inline struct page *compound_trans_head(struct page *page)
{
if (PageTail(page)) {
struct page *head;
head = page->first_page;
smp_rmb();
/*
* head may be a dangling pointer.
* __split_huge_page_refcount clears PageTail before
* overwriting first_page, so if PageTail is still
* there it means the head pointer isn't dangling.
*/
if (PageTail(page))
return head;
}
return page;
}
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
#define HPAGE_PMD_SHIFT ({ BUG(); 0; })
#define HPAGE_PMD_MASK ({ BUG(); 0; })
@ -144,6 +161,7 @@ static inline int split_huge_page(struct page *page)
do { } while (0)
#define wait_split_huge_page(__anon_vma, __pmd) \
do { } while (0)
#define compound_trans_head(page) compound_head(page)
static inline int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
{

15
mm/ksm.c
View file

@ -415,20 +415,11 @@ out:
static struct page *page_trans_compound_anon(struct page *page)
{
if (PageTransCompound(page)) {
struct page *head;
head = compound_head(page);
struct page *head = compound_trans_head(page);
/*
* head may be a dangling pointer.
* __split_huge_page_refcount clears PageTail
* before overwriting first_page, so if
* PageTail is still there it means the head
* pointer isn't dangling.
* head may actually be splitted and freed from under
* us but it's ok here.
*/
if (head != page) {
smp_rmb();
if (!PageTransCompound(page))
return NULL;
}
if (PageAnon(head))
return head;
}

32
virt/kvm/kvm_main.c
View file

@ -104,35 +104,25 @@ static pfn_t fault_pfn;
inline int kvm_is_mmio_pfn(pfn_t pfn)
{
if (pfn_valid(pfn)) {
struct page *head;
int reserved;
struct page *tail = pfn_to_page(pfn);
head = compound_head(tail);
struct page *head = compound_trans_head(tail);
reserved = PageReserved(head);
if (head != tail) {
smp_rmb();
/*
* head may be a dangling pointer.
* __split_huge_page_refcount clears PageTail
* before overwriting first_page, so if
* PageTail is still there it means the head
* pointer isn't dangling.
* "head" is not a dangling pointer
* (compound_trans_head takes care of that)
* but the hugepage may have been splitted
* from under us (and we may not hold a
* reference count on the head page so it can
* be reused before we run PageReferenced), so
* we've to check PageTail before returning
* what we just read.
*/
if (PageTail(tail)) {
/*
* the "head" is not a dangling
* pointer but the hugepage may have
* been splitted from under us (and we
* may not hold a reference count on
* the head page so it can be reused
* before we run PageReferenced), so
* we've to recheck PageTail before
* returning what we just read.
*/
int reserved = PageReserved(head);
smp_rmb();
if (PageTail(tail))
return reserved;
}
}
return PageReserved(tail);
}