From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751967AbeCPKFP (ORCPT ); Fri, 16 Mar 2018 06:05:15 -0400 Received: from mga07.intel.com ([134.134.136.100]:23168 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750982AbeCPKFO (ORCPT ); Fri, 16 Mar 2018 06:05:14 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,315,1517904000"; d="scan'208";a="183348583" Date: Fri, 16 Mar 2018 13:05:10 +0300 From: "Kirill A. Shutemov" To: Andrew Morton Cc: Laura Abbott , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/khugepaged: Convert VM_BUG_ON() to collapse fail Message-ID: <20180316100510.gedh6svgemb5jrmj@black.fi.intel.com> References: <20180315152353.27989-1-kirill.shutemov@linux.intel.com> <20180315160453.dff17cfe3dca056dabc98b9e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180315160453.dff17cfe3dca056dabc98b9e@linux-foundation.org> User-Agent: NeoMutt/20170714-126-deb55f (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 15, 2018 at 11:04:53PM +0000, Andrew Morton wrote: > On Thu, 15 Mar 2018 18:23:53 +0300 "Kirill A. Shutemov" wrote: > > > khugepaged is not yet able to convert PTE-mapped huge pages back to PMD > > mapped. We do not collapse such pages. See check khugepaged_scan_pmd(). > > > > But if between khugepaged_scan_pmd() and __collapse_huge_page_isolate() > > somebody managed to instantiate THP in the range and then split the PMD > > back to PTEs we would have a problem -- VM_BUG_ON_PAGE(PageCompound(page)) > > will get triggered. > > > > It's possible since we drop mmap_sem during collapse to re-take for > > write. > > > > Replace the VM_BUG_ON() with graceful collapse fail. > > > > Signed-off-by: Kirill A. Shutemov > > Fixes: b1caa957ae6d ("khugepaged: ignore pmd tables with THP mapped with ptes") > > Jan 2016. Do we need a cc:stable? Yes, please. I forgot to put it. -- Kirill A. Shutemov