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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 30 Mar 2020 11:26:13 +0100 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 02UAQOFg59113556 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Mar 2020 10:26:24 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D3E952050; Mon, 30 Mar 2020 10:26:24 +0000 (GMT) Received: from linux.ibm.com (unknown [9.148.206.230]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTPS id B189B5204F; Mon, 30 Mar 2020 10:26:21 +0000 (GMT) Date: Mon, 30 Mar 2020 13:26:19 +0300 From: Mike Rapoport To: Michal Hocko Subject: Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA References: <1585420282-25630-1-git-send-email-Hoan@os.amperecomputing.com> <20200330074246.GA14243@dhcp22.suse.cz> <20200330092127.GB30942@linux.ibm.com> <20200330095843.GF14243@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200330095843.GF14243@dhcp22.suse.cz> X-TM-AS-GCONF: 00 x-cbid: 20033010-0020-0000-0000-000003BE2E3C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20033010-0021-0000-0000-00002216C92E Message-Id: <20200330102619.GC30942@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.645 definitions=2020-03-30_01:2020-03-27, 2020-03-30 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 bulkscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=1 mlxlogscore=731 adultscore=0 malwarescore=0 mlxscore=0 priorityscore=1501 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003300091 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mmorana@amperecomputing.com, Catalin Marinas , Heiko Carstens , "open list:MEMORY MANAGEMENT" , Paul Mackerras , "H. Peter Anvin" , sparclinux@vger.kernel.org, Alexander Duyck , linux-s390@vger.kernel.org, x86@kernel.org, Christian Borntraeger , Ingo Molnar , Hoan Tran , Pavel Tatashin , lho@amperecomputing.com, Vasily Gorbik , Vlastimil Babka , Will Deacon , Borislav Petkov , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Oscar Salvador , linux-kernel@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Mar 30, 2020 at 11:58:43AM +0200, Michal Hocko wrote: > On Mon 30-03-20 12:21:27, Mike Rapoport wrote: > > On Mon, Mar 30, 2020 at 09:42:46AM +0200, Michal Hocko wrote: > > > On Sat 28-03-20 11:31:17, Hoan Tran wrote: > > > > In NUMA layout which nodes have memory ranges that span across other nodes, > > > > the mm driver can detect the memory node id incorrectly. > > > > > > > > For example, with layout below > > > > Node 0 address: 0000 xxxx 0000 xxxx > > > > Node 1 address: xxxx 1111 xxxx 1111 > > > > > > > > Note: > > > > - Memory from low to high > > > > - 0/1: Node id > > > > - x: Invalid memory of a node > > > > > > > > When mm probes the memory map, without CONFIG_NODES_SPAN_OTHER_NODES > > > > config, mm only checks the memory validity but not the node id. > > > > Because of that, Node 1 also detects the memory from node 0 as below > > > > when it scans from the start address to the end address of node 1. > > > > > > > > Node 0 address: 0000 xxxx xxxx xxxx > > > > Node 1 address: xxxx 1111 1111 1111 > > > > > > > > This layout could occur on any architecture. Most of them enables > > > > this config by default with CONFIG_NUMA. This patch, by default, enables > > > > CONFIG_NODES_SPAN_OTHER_NODES or uses early_pfn_in_nid() for NUMA. > > > > > > I am not opposed to this at all. It reduces the config space and that is > > > a good thing on its own. The history has shown that meory layout might > > > be really wild wrt NUMA. The config is only used for early_pfn_in_nid > > > which is clearly an overkill. > > > > > > Your description doesn't really explain why this is safe though. The > > > history of this config is somehow messy, though. Mike has tried > > > to remove it a94b3ab7eab4 ("[PATCH] mm: remove arch independent > > > NODES_SPAN_OTHER_NODES") just to be reintroduced by 7516795739bd > > > ("[PATCH] Reintroduce NODES_SPAN_OTHER_NODES for powerpc") without any > > > reasoning what so ever. This doesn't make it really easy see whether > > > reasons for reintroduction are still there. Maybe there are some subtle > > > dependencies. I do not see any TBH but that might be burried deep in an > > > arch specific code. > > > > Well, back then early_pfn_in_nid() was arch-dependant, today everyone > > except ia64 rely on HAVE_MEMBLOCK_NODE_MAP. > > What would it take to make ia64 use HAVE_MEMBLOCK_NODE_MAP? I would > really love to see that thing go away. It is causing problems when > people try to use memblock api. Sorry, my bad, ia64 does not have NODES_SPAN_OTHER_NODES, but it does have HAVE_MEMBLOCK_NODE_MAP. I remember I've tried killing HAVE_MEMBLOCK_NODE_MAP, but I've run into some problems and then I've got distracted. I too would like to have HAVE_MEMBLOCK_NODE_MAP go away, maybe I'll take another look at it. > > So, if the memblock node map > > is correct, that using CONFIG_NUMA instead of CONFIG_NODES_SPAN_OTHER_NODES > > would only mean that early_pfn_in_nid() will cost several cycles more on > > architectures that didn't select CONFIG_NODES_SPAN_OTHER_NODES (i.e. arm64 > > and sh). > > Do we have any idea on how much of an overhead that is? Because this is > per each pfn so it can accumulate a lot! It's O(log(N)) where N is the amount of the memory banks (ie. memblock.memory.cnt) > > Agian, ia64 is an exception here. > > Thanks for the clarification! > -- > Michal Hocko > SUSE Labs -- Sincerely yours, Mike.