From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f46.google.com (mail-la0-f46.google.com [209.85.215.46]) by kanga.kvack.org (Postfix) with ESMTP id 685176B0038 for ; Thu, 14 May 2015 14:50:33 -0400 (EDT) Received: by laat2 with SMTP id t2so81257385laa.1 for ; Thu, 14 May 2015 11:50:32 -0700 (PDT) Received: from mail-la0-f45.google.com (mail-la0-f45.google.com. [209.85.215.45]) by mx.google.com with ESMTPS id g10si15087467lam.78.2015.05.14.11.50.30 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 May 2015 11:50:31 -0700 (PDT) Received: by laat2 with SMTP id t2so81255514laa.1 for ; Thu, 14 May 2015 11:50:30 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <55532CB0.6070400@yandex-team.ru> References: <20150512090156.24768.2521.stgit@buzz> <20150512094303.24768.10282.stgit@buzz> <55532CB0.6070400@yandex-team.ru> Date: Thu, 14 May 2015 19:50:30 +0100 Message-ID: Subject: Re: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages mapped only here From: Mark Williamson Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, Naoya Horiguchi , kernel list , Andrew Morton , Pavel Emelyanov , Linux API , Andy Lutomirski , Vlastimil Babka , Pavel Machek , Mark Seaborn , "Kirill A. Shutemov" , Linus Torvalds , Daniel James , Finn Grimwood Hi Konstantin, On Wed, May 13, 2015 at 11:51 AM, Konstantin Khlebnikov wrote: > On 12.05.2015 15:05, Mark Williamson wrote: >> 1. I was hoping we'd be able to backport a compatible fix to older >> kernels that might adopt the pagemap permissions change. Using the V2 >> format flags rules out doing this for kernels that are too old to have >> soft-dirty, I think. >> >> 2. From our software's PoV, I feel it's worth noting that it doesn't >> strictly fix ABI compatibility, though I realise that's probably not >> your primary concern here. We'll need to modify our code to write the >> clear_refs file but that change is OK for us if it's the preferred >> solution. > I prefer to backport v2 format (except soft-dirty bit and clear_refs) > into older kernels. Page-shift bits are barely used so nobody will see > the difference. My concern was whether a change to format would be acceptable to include in the various -stable kernels; they are already including the additional protections on pagemap, so we're starting to need our fallback mode in distributions. Do you think that such a patch would be acceptable there? (As an application vendor we're likely to be particularly stuck with what the commercial distributions decide to ship, which is why I'm trying to keep an eye on this) I appreciate that this is a slightly administrative concern! I definitely like the technical approach of this code and it seems to work fine for us. Thanks, Mark -- 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