Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752674AbbHUTbS (ORCPT ); Fri, 21 Aug 2015 15:31:18 -0400 Received: from mail-wi0-f174.google.com ([209.85.212.174]:35982 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022AbbHUTbR (ORCPT ); Fri, 21 Aug 2015 15:31:17 -0400 Date: Fri, 21 Aug 2015 22:31:09 +0300 From: "Kirill A. Shutemov" 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 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: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 874 Lines: 23 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/