Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756310AbZJAKys (ORCPT ); Thu, 1 Oct 2009 06:54:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756283AbZJAKyr (ORCPT ); Thu, 1 Oct 2009 06:54:47 -0400 Received: from mk-filter-3-a-1.mail.uk.tiscali.com ([212.74.100.54]:4033 "EHLO mk-filter-3-a-1.mail.uk.tiscali.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756276AbZJAKyq (ORCPT ); Thu, 1 Oct 2009 06:54:46 -0400 X-Trace: 265406197/mk-filter-3.mail.uk.tiscali.com/B2C/$b2c-THROTTLED-DYNAMIC/b2c-CUSTOMER-DYNAMIC-IP/80.41.44.42/None/hugh.dickins@tiscali.co.uk X-SBRS: None X-RemoteIP: 80.41.44.42 X-IP-MAIL-FROM: hugh.dickins@tiscali.co.uk X-SMTP-AUTH: X-MUA: X-IP-BHB: Once X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AtoEACYnxEpQKSwq/2dsb2JhbACBUdR/hCgE X-IronPort-AV: E=Sophos;i="4.44,487,1249254000"; d="scan'208";a="265406197" Date: Thu, 1 Oct 2009 11:54:34 +0100 (BST) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Christoph Lameter cc: KAMEZAWA Hiroyuki , Wu Fengguang , Nigel Cunningham , LKML , "linux-mm@kvack.org" Subject: Re: No more bits in vm_area_struct's vm_flags. In-Reply-To: Message-ID: References: <4AB9A0D6.1090004@crca.org.au> <20090924100518.78df6b93.kamezawa.hiroyu@jp.fujitsu.com> <4ABC80B0.5010100@crca.org.au> <20090925174009.79778649.kamezawa.hiroyu@jp.fujitsu.com> <4AC0234F.2080808@crca.org.au> <20090928120450.c2d8a4e2.kamezawa.hiroyu@jp.fujitsu.com> <20090928033624.GA11191@localhost> <20090928125705.6656e8c5.kamezawa.hiroyu@jp.fujitsu.com> <20090929105735.06eea1ee.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1649 Lines: 38 On Tue, 29 Sep 2009, Christoph Lameter wrote: > > Another concern that has not been discussed is the increased cache > footprint due to a slightly enlarged vm data working set (there is also a > corresponding icache issue since additional accesses are needed). Using unsigned long long vm_flags makes no difference to cache footprint on 64-bit systems, being a no-op there; and I think these days, though we sure like our 32-bit systems to run well, we're not so anxious about saving every last cycle on them. > > Could we stick with the current size and do combinations of flags like we > do with page flags? Are we doing that? If you have some example like, when PG_slab is set then PG_owner_priv_1 means such-and-such, but if not not: okay, I'm fine with that. But if you're saying something like, if PG_reclaim is set at the same time as PG_buddy, then they mean the page is not a buddy or under reclaim, but brokenbacked: then I'm a bit (or even 32 bits) worried. > VM_HUGETLB cannot grow up and down f.e. and there are > certainly lots of other impossible combinations that can be used to put > more information into the flags. Where it makes sense, where it's understandable, okay: there may be a few which could naturally use combinations. But in general, no, I think we'd be asking for endless maintenance trouble if we change the meaning of some flags according to other flags. Hugh -- 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/