From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 062668D0039 for ; Fri, 21 Jan 2011 13:11:44 -0500 (EST) Date: Fri, 21 Jan 2011 18:36:18 +0100 From: Andrea Arcangeli Subject: Re: [PATCH 1/3] When migrate_pages returns 0, all pages must have been released Message-ID: <20110121173618.GH9506@random.random> References: <20110120182444.GA9506@random.random> <20110120212841.GB9506@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 Fri, Jan 21, 2011 at 10:11:03AM -0600, Christoph Lameter wrote: > On Thu, 20 Jan 2011, Andrea Arcangeli wrote: > > > 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). > > Ahh yes we removed the putback_lru_pages call from migrate_pages() > and broke the existing release logic. The caller has to call > putback_release_pages() as per commit putback_lru_paeges > cf608ac19c95804dc2df43b1f4f9e068aa9034ab That is the very commit that introduced the two bugs that I've fixed by code review. > > If that is still the case then we still have the double free. The caller only calls putback_lru_pages if ret != 0 (the two cases you refer to happen with ret = 0). Even if caller unconditionally calls putback_lru_pages (kind of what compaction did), it can't double free because migrate_pages already unlinked the pages before calling putback_lru_page(page), so there's no way to do a double free (however if the caller unconditionally called putback_lru_pages there would be no memleak to fix, but it doesn't). > Could we please document the calling conventions exactly in the source? > Right now it says that the caller should call putback_lru_pages(). The caller should call putback_lru_pages only if ret != 0. Minchan this is your commit we're discussing can you check the commentary? Thanks! Andrea -- 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