From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 963256B0003 for ; Fri, 16 Mar 2018 06:05:15 -0400 (EDT) Received: by mail-pl0-f69.google.com with SMTP id z11-v6so5125446plo.21 for ; Fri, 16 Mar 2018 03:05:15 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id 98-v6si5913698pls.244.2018.03.16.03.05.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Mar 2018 03:05:14 -0700 (PDT) Date: Fri, 16 Mar 2018 13:05:10 +0300 From: "Kirill A. Shutemov" 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> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Laura Abbott , linux-mm@kvack.org, 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