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mm: improve find_lock_page 

find_lock_page does not need to recheck ->index because if the page is in the
right mapping then the index must be the same.  Also, tree_lock does not need
to be retaken after the page is locked in order to test that ->mapping has not
changed, because holding the page lock pins its mapping.

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 2007-10-16 01:24:41 -07:00 committed by Linus Torvalds
parent 0012818810
commit 45726cb43d
1 changed files with 5 additions and 4 deletions
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9
mm/filemap.c
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@ -621,26 +621,27 @@ struct page *find_lock_page(struct address_space *mapping,
{
struct page *page;
read_lock_irq(&mapping->tree_lock);
repeat:
read_lock_irq(&mapping->tree_lock);
page = radix_tree_lookup(&mapping->page_tree, offset);
if (page) {
page_cache_get(page);
if (TestSetPageLocked(page)) {
read_unlock_irq(&mapping->tree_lock);
__lock_page(page);
read_lock_irq(&mapping->tree_lock);
/* Has the page been truncated while we slept? */
if (unlikely(page->mapping != mapping ||
page->index != offset)) {
if (unlikely(page->mapping != mapping)) {
unlock_page(page);
page_cache_release(page);
goto repeat;
}
VM_BUG_ON(page->index != offset);
goto out;
}
}
read_unlock_irq(&mapping->tree_lock);
out:
return page;
}
EXPORT_SYMBOL(find_lock_page);