From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932588AbbDJR4U (ORCPT ); Fri, 10 Apr 2015 13:56:20 -0400 Received: from mail-pa0-f53.google.com ([209.85.220.53]:34125 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755820AbbDJR4R (ORCPT ); Fri, 10 Apr 2015 13:56:17 -0400 Date: Fri, 10 Apr 2015 10:56:07 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Susheel Khiani cc: akpm@linux-foundation.org, peterz@infradead.org, neilb@suse.de, dhowells@redhat.com, hughd@google.com, paulmcquad@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [Question] ksm: rmap_item pointing to some stale vmas In-Reply-To: <55268741.8010301@codeaurora.org> Message-ID: References: <55268741.8010301@codeaurora.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 9 Apr 2015, Susheel Khiani wrote: > Hi, > > We are seeing an issue during try_to_unmap_ksm where in call to > try_to_unmap_one is failing. > > try_to_unmap_ksm in this particular case is trying to go through vmas > associated with each rmap_item->anon_vma. What we see is this that the > corresponding page is not mapped to any of the vmas associated with 2 > rmap_item. > > The associated rmap_item in this case looks like pointing to some valid vma > but the said page is not found to be mapped under it. try_to_unmap_one thus > fails to find valid ptes for these vmas. > > At the same time we can see that the page actually is mapped in 2 separate > and different vmas which are not part of rmap_item associated with page. > > So whether rmap_item is pointing to some stale vmas and now the mapping has > changed? Or there is something else going on here. > p > Any pointer would be appreciated. I expected to be able to argue this away, but no: I think you've found a bug, and I think I get it too. I have no idea what's wrong at this point, will set aside some time to investigate, and report back. Which kernel are you using? try_to_unmap_ksm says v3.13 or earlier. Probably doesn't affect the bug, but may affect the patch you'll need. Hugh