From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262162AbUKQC3X (ORCPT ); Tue, 16 Nov 2004 21:29:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262163AbUKQC3X (ORCPT ); Tue, 16 Nov 2004 21:29:23 -0500 Received: from fw.osdl.org ([65.172.181.6]:13713 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S262162AbUKQC3D (ORCPT ); Tue, 16 Nov 2004 21:29:03 -0500 Date: Tue, 16 Nov 2004 18:28:41 -0800 From: Andrew Morton To: Linus Torvalds Cc: dhowells@redhat.com, hch@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] Making compound pages mandatory Message-Id: <20041116182841.4ff7f2e5.akpm@osdl.org> In-Reply-To: References: <2315.1100630906@redhat.com> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds wrote: > > > > On Tue, 16 Nov 2004, David Howells wrote: > > > > Do you have any objection to compound pages being made mandatory, even without > > HUGETLB support? > > I haven't really looked into it, so I cannot make an informed decision. > How big is the overhead? And what's the _point_, since we don't seem to > need them normally, but the code is there for people who _do_ need them? Yes, it's just the single pointer chase. Probably that's the common case now, because everyone will be enabling hugepages on lots of architectures. But still, the non-compound code is well tested too, and leaving it in place does make a little microoptimisation available to those who want it, so I don't see a reason yet to make compound pages compulsory. So I'd suggest that we make compound pages conditional on a new CONFIG_COMPOUND_PAGE and make that equal to HUGETLB_PAGE || !MMU.