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Commit 45726cb4 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 00128188

mm/filemap.c

+5 −4
Original line number Diff line number Diff line
@@ -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);