From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 90D886007B8 for ; Mon, 3 May 2010 14:14:10 -0400 (EDT) Date: Mon, 3 May 2010 20:13:40 +0200 From: Andrea Arcangeli Subject: Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma_lock Message-ID: <20100503181340.GH19891@random.random> References: <20100503121743.653e5ecc@annuminas.surriel.com> <20100503121847.7997d280@annuminas.surriel.com> <4BDEFF9E.6080508@redhat.com> <4BDF0ECC.5080902@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BDF0ECC.5080902@redhat.com> Sender: owner-linux-mm@kvack.org To: Rik van Riel Cc: Linus Torvalds , akpm@linux-foundation.org, Mel Gorman , Linux-MM , LKML , Minchan Kim , KAMEZAWA Hiroyuki , Christoph Lameter List-ID: > > Btw, Mel's patch doesn't really match the description of 2/2. 2/2 says > > that all pages must always be findable in rmap. Mel's patch seems to > > explicitly say "we want to ignore that thing that is busy for execve". Are > > we just avoiding a BUG_ON()? Is perhaps the BUG_ON() buggy? > > I have no good answer to this question. > > Mel? Andrea? If try_to_unmap is allowed to establish the migration pte, then such pte has to remain reachable through rmap_walk at all times after that, or migration_entry_wait will crash because it notices the page has been migrated already (PG_lock not set) but there is still a migration pte established. (remove_migration_pte like split_huge_page isn't allowed to fail finding all migration ptes mapping a page during the rmap walk) It's not false positive BUG_ON if that's what you mean, removing the BUG_ON would still lead to infinite hang waiting on a migration pte that shouldn't be there anymore. -- 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