From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) by ozlabs.org (Postfix) with ESMTP id 6F1482C0092 for ; Fri, 6 Dec 2013 22:30:10 +1100 (EST) Date: Fri, 6 Dec 2013 11:30:03 +0000 From: Mel Gorman To: "Aneesh Kumar K.V" 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 In-Reply-To: <1386268702-30806-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Cc: riel@redhat.com, paulus@samba.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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