From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f177.google.com (mail-wi0-f177.google.com [209.85.212.177]) by kanga.kvack.org (Postfix) with ESMTP id 58EE36B0253 for ; Fri, 21 Aug 2015 15:31:18 -0400 (EDT) Received: by widdq5 with SMTP id dq5so23617701wid.0 for ; Fri, 21 Aug 2015 12:31:17 -0700 (PDT) Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com. [209.85.212.174]) by mx.google.com with ESMTPS id un9si16685383wjc.60.2015.08.21.12.31.16 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Aug 2015 12:31:16 -0700 (PDT) Received: by widdq5 with SMTP id dq5so150183wid.1 for ; Fri, 21 Aug 2015 12:31:16 -0700 (PDT) Date: Fri, 21 Aug 2015 22:31:09 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust Message-ID: <20150821193109.GA14785@node.dhcp.inet.fi> References: <1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com> <1439976106-137226-5-git-send-email-kirill.shutemov@linux.intel.com> <20150820163643.dd87de0c1a73cb63866b2914@linux-foundation.org> <20150821121028.GB12016@node.dhcp.inet.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Andrew Morton , "Kirill A. Shutemov" , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Johannes Weiner , Michal Hocko , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri, Aug 21, 2015 at 11:11:27AM -0500, Christoph Lameter wrote: > On Fri, 21 Aug 2015, Kirill A. Shutemov wrote: > > > > Is this really true? For example if it's a slab page, will that page > > > ever be inspected by code which is looking for the PageTail bit? > > > > +Christoph. > > > > What we know for sure is that space is not used in tail pages, otherwise > > it would collide with current compound_dtor. > > Sl*b allocators only do a virt_to_head_page on tail pages. The question was whether it's safe to assume that the bit 0 is always zero in the word as this bit will encode PageTail(). -- Kirill A. Shutemov -- 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