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[73.69.118.222]) by smtp.gmail.com with ESMTPSA id v10-v6sm9208266qkv.90.2018.10.16.14.06.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Oct 2018 14:06:49 -0700 (PDT) Subject: Re: [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant To: Alexander Duyck , linux-mm@kvack.org, akpm@linux-foundation.org Cc: pavel.tatashin@microsoft.com, mhocko@suse.com, dave.jiang@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, davem@davemloft.net, yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com, rppt@linux.vnet.ibm.com, vbabka@suse.cz, sparclinux@vger.kernel.org, dan.j.williams@intel.com, ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net, mingo@kernel.org, kirill.shutemov@linux.intel.com References: <20181015202456.2171.88406.stgit@localhost.localdomain> <20181015202703.2171.40829.stgit@localhost.localdomain> From: Pavel Tatashin Message-ID: <06e4428b-860e-1e66-defd-77666fcfa0c5@gmail.com> Date: Tue, 16 Oct 2018 17:06:48 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/16/18 4:49 PM, Alexander Duyck wrote: > On 10/16/2018 1:33 PM, Pavel Tatashin wrote: >> >> >> On 10/15/18 4:27 PM, Alexander Duyck wrote: >>> As best as I can tell the meminit_pfn_in_nid call is completely >>> redundant. >>> The deferred memory initialization is already making use of >>> for_each_free_mem_range which in turn will call into __next_mem_range >>> which >>> will only return a memory range if it matches the node ID provided >>> assuming >>> it is not NUMA_NO_NODE. >>> >>> I am operating on the assumption that there are no zones or pgdata_t >>> structures that have a NUMA node of NUMA_NO_NODE associated with >>> them. If >>> that is the case then __next_mem_range will never return a memory range >>> that doesn't match the zone's node ID and as such the check is >>> redundant. >>> >>> So one piece I would like to verfy on this is if this works for ia64. >>> Technically it was using a different approach to get the node ID, but it >>> seems to have the node ID also encoded into the memblock. So I am >>> assuming this is okay, but would like to get confirmation on that. >>> >>> Signed-off-by: Alexander Duyck >> >> If I am not mistaken, this code is for systems with memory interleaving. >> Quick looks shows that x86, powerpc, s390, and sparc have it set. >> >> I am not sure about other arches, but at least on SPARC, there are some >> processors with memory interleaving feature: >> >> http://www.fujitsu.com/global/products/computing/servers/unix/sparc-enterprise/technology/performance/memory.html >> >> >> Pavel > > I get what it is for. However as best I can tell the check is actually > redundant. In the case of the deferred page initialization we are > already pulling the memory regions via "for_each_free_mem_range". That > function is already passed a NUMA node ID. Because of that we are > already checking the memory range to determine if it is in the node or > not. As such it doesn't really make sense to go through for each PFN and > then go back to the memory range and see if the node matches or not. > Agree, it looks redundant, nice clean-up, I like it. Reviewed-by: Pavel Tatashin Thank you, Pavel > You can take a look at __next_mem_range which is called by > for_each_free_mem_range and passed &memblock.memory and > &memblock.reserved to avoid: > https://elixir.bootlin.com/linux/latest/source/mm/memblock.c#L899 > > Then you can work your way through: > meminit_pfn_in_nid(pfn, node, state) >  __early_pfn_to_nid(pfn, state) >   memblock_search_pfn_nid(pfn, &start_pfn, &end_pfn) >    memblock_search(&memblock.memory, pfn) > > From what I can tell the deferred init is going back through the > memblock.memory list we pulled this range from and just validating it > against itself. This makes sense for the standard init as that is just > going from start_pfn->end_pfn, but for the deferred init we are pulling > the memory ranges ahead of time so we shouldn't need to re-validate the > memory that is contained within that range.