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Violators will be prosecuted for from ; Mon, 30 Mar 2020 11:26:20 +0100 Date: Mon, 30 Mar 2020 13:26:19 +0300 From: Mike Rapoport 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> Message-Id: <20200330102619.GC30942@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Michal Hocko Cc: Hoan Tran , Catalin Marinas , Will Deacon , Andrew Morton , Vlastimil Babka , Oscar Salvador , Pavel Tatashin , Alexander Duyck , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "David S. Miller" , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , "open list:MEMORY MANAGEMENT" , linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, lho@amperecomputing.com, mmorana@amperecomputing.com 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.