From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 2 Aug 2007 06:55:46 +0200 From: Nick Piggin Subject: [patch] mm: improve find_lock_page Message-ID: <20070802045546.GC13591@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Linux Memory Management List , Hugh Dickins List-ID: OK this patch isn't really going to help performance much (it's all slowpath stuff), but it does help to clarify the locking. -- 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 Index: linux-2.6/mm/filemap.c =================================================================== --- linux-2.6.orig/mm/filemap.c +++ linux-2.6/mm/filemap.c @@ -621,26 +621,27 @@ struct page *find_lock_page(struct addre { 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); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org