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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 <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Avi Kivity <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andrea Arcangeli 2011-01-13 15:47:20 -08:00 • committed by Linus Torvalds
commit 22e5c47ee2
3 changed files with 35 additions and 36 deletions
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38
virt/kvm/kvm_main.c
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@ -104,34 +104,24 @@ 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;
}
smp_rmb();
if (PageTail(tail))
return reserved;
}
return PageReserved(tail);
}