From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id E77F18D0069 for ; Thu, 20 Jan 2011 16:29:10 -0500 (EST) Date: Thu, 20 Jan 2011 22:28:41 +0100 From: Andrea Arcangeli Subject: Re: [PATCH 1/3] When migrate_pages returns 0, all pages must have been released Message-ID: <20110120212841.GB9506@random.random> References: <20110120182444.GA9506@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Christoph Lameter Cc: Minchan Kim , Andrew Morton , linux-mm , LKML , Mel Gorman List-ID: On Thu, Jan 20, 2011 at 12:49:15PM -0600, Christoph Lameter wrote: > On Thu, 20 Jan 2011, Andrea Arcangeli wrote: > > > Hello, > > > > On Thu, Jan 20, 2011 at 11:30:35AM -0600, Christoph Lameter wrote: > > > On Fri, 21 Jan 2011, Minchan Kim wrote: > > > > > > > diff --git a/mm/migrate.c b/mm/migrate.c > > > > index 46fe8cc..7d34237 100644 > > > > --- a/mm/migrate.c > > > > +++ b/mm/migrate.c > > > > @@ -772,6 +772,7 @@ uncharge: > > > > unlock: > > > > unlock_page(page); > > > > > > > > +move_newpage: > > > > if (rc != -EAGAIN) { > > > > /* > > > > * A page that has been migrated has all references > > > > @@ -785,8 +786,6 @@ unlock: > > > > putback_lru_page(page); > > > > } > > > > > > > > -move_newpage: > > > > - > > > > /* > > > > * Move the new page to the LRU. If migration was not successful > > > > * then this will free the page. > > > > > > > > > > What does this do? Not covered by the description. > > > > It makes a difference for the two goto move_newpage, when rc = > > 0. Otherwise the function will return 0, despite > > putback_lru_page(page) wasn't called (and the caller of migrate_pages > > won't call putback_lru_pages if migrate_pages returned 0). > > Think about the difference: > > Moving the move_newpage will now cause another removal and freeing of the > page if rc != -EAGAIN. The only ones doing "goto move_newpage" after the first two memleaks that are fixed by this patch are always run with rc = -EAGAIN. So this makes a difference only for the first two which were leaking memory before. > The first goto move_newpage (because page count is 1) will now mean that > the page is freed twice. One because of the rc != EAGAIN branch and then > another time by the following putback_lru_page(). Which following putback_lru_page()? You mean putback_lru_page(newpage)? That is for the newly allocated page (allocated at the very top, so always needed), it's not relevant to the page_count(page) = 1. The page_count 1 is hold by the caller, so it's leaking memory right now (for everything but compaction). -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org