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mm: page lock use lock bitops

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trylock_page, unlock_page open and close a critical section. Hence,
we can use the lock bitops to get the desired memory ordering.

Also, mark trylock as likely to succeed (and remove the annotation from
callers).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin
2008-10-18 20:26:59 -07:00
committed by Linus Torvalds
parent a978d6f521
commit 8413ac9d8c
3 changed files with 7 additions and 10 deletions
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13
mm/filemap.c
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@@ -573,17 +573,14 @@ EXPORT_SYMBOL(wait_on_page_bit);
* mechananism between PageLocked pages and PageWriteback pages is shared.
* But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
*
* The first mb is necessary to safely close the critical section opened by the
* test_and_set_bit() to lock the page; the second mb is necessary to enforce
* ordering between the clear_bit and the read of the waitqueue (to avoid SMP
* races with a parallel wait_on_page_locked()).
* The mb is necessary to enforce ordering between the clear_bit and the read
* of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
*/
void unlock_page(struct page *page)
{
smp_mb__before_clear_bit();
if (!test_and_clear_bit(PG_locked, &page->flags))
BUG();
smp_mb__after_clear_bit();
VM_BUG_ON(!PageLocked(page));
clear_bit_unlock(PG_locked, &page->flags);
smp_mb__after_clear_bit();
wake_up_page(page, PG_locked);
}
EXPORT_SYMBOL(unlock_page);