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Commit 22e5c47e authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

thp: add compound_trans_head() helper 



Cleanup some code with common compound_trans_head helper.

Signed-off-by: default avatarAndrea 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 29ad768c

include/linux/huge_mm.h

+18 −0
Original line number Diff line number Diff line
@@ -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)

{

mm/ksm.c

+3 −12
Original line number Diff line number Diff line
@@ -415,20 +415,11 @@ static void break_cow(struct rmap_item *rmap_item) 
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;

	}

virt/kvm/kvm_main.c

+14 −24
Original line number Diff line number Diff line
@@ -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.

			 */

			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.

			 * "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.

			 */

				int reserved = PageReserved(head);

			smp_rmb();

			if (PageTail(tail))

				return reserved;

		}

		}

		return PageReserved(tail);

	}