From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f51.google.com (mail-ee0-f51.google.com [74.125.83.51]) by kanga.kvack.org (Postfix) with ESMTP id 3B1546B0035 for ; Fri, 6 Dec 2013 06:30:09 -0500 (EST) Received: by mail-ee0-f51.google.com with SMTP id b15so235569eek.10 for ; Fri, 06 Dec 2013 03:30:08 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTP id w6si14380585eeg.132.2013.12.06.03.30.08 for ; Fri, 06 Dec 2013 03:30:08 -0800 (PST) Date: Fri, 6 Dec 2013 11:30:03 +0000 From: Mel Gorman Subject: Re: [PATCH -V3] mm: Move change_prot_numa outside CONFIG_ARCH_USES_NUMA_PROT_NONE Message-ID: <20131206113003.GP11295@suse.de> References: <1386268702-30806-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1386268702-30806-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: benh@kernel.crashing.org, paulus@samba.org, riel@redhat.com, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org On Fri, Dec 06, 2013 at 12:08:22AM +0530, Aneesh Kumar K.V wrote: > From: "Aneesh Kumar K.V" > > change_prot_numa should work even if _PAGE_NUMA != _PAGE_PROTNONE. > On archs like ppc64 that don't use _PAGE_PROTNONE and also have > a separate page table outside linux pagetable, we just need to > make sure that when calling change_prot_numa we flush the > hardware page table entry so that next page access result in a numa > fault. > > We still need to make sure we use the numa faulting logic only > when CONFIG_NUMA_BALANCING is set. This implies the migrate-on-fault > (Lazy migration) via mbind will only work if CONFIG_NUMA_BALANCING > is set. > > Signed-off-by: Aneesh Kumar K.V You're right on that there is no direct dependance on numa balancing and use of prot_none. The BUILD_BUG_ON was to flag very clearly that arches wanting to support automatic NUMA balancing must ensure such things as o _PAGE_NUMA is defined o setting _PAGE_NUMA traps a fault and the fault can be uniquely identified as being a numa hinting fault o that pte_present still returns true for pte_numa pages even though the underlying present bit may be cleared. Otherwise operations like following and copying ptes will get confused o shortly, arches will also need to avoid taking references on pte_numa pages in get_user_pages to account for hinting faults properly I guess the _PAGE_NUMA parts will already be caught by other checks and the rest will fall out during testing so it's ok to remove. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs -- 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