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 <alexander.h.duyck@xxxxxxxxxxxxxxx> >> >> 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 <pavel.tatashin@xxxxxxxxxxxxx> 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.
