On 08/19/2020 03:11 PM, Jonathan Cameron wrote: > On Wed, 19 Aug 2020 10:31:18 +0530 > Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote: > >> Hello Jonathan, > > Hi Anshuman, > >> >> On 07/08/2020 05:08 PM, Jonathan Cameron wrote: >>> Unfortunately we are currently calling numa_alloc_distance well before we call >>> setup_node_to_cpu_mask_map means that nr_node_ids is set to MAX_NUMNODES. >>> This wastes a bit of memory and is confusing to the reader. >> >> With defconfig where CONFIG_NODES_SHIFT = 2 i.e MAX_NUMNODES = 4, the total >> numa_distance size is 16 bytes (individual entries here are just u8). > > That's another issue to tidy up. The current defconfig isn't big enough to > support existing platforms (we are shipping 8 node systems), > let alone next generation. Bit of an open question on how far to push it up > though. Perhaps 64? Given CXL we are probably going to soon see systems with > a lot more nodes. I'll send a patch for that and we can argue the exact > value then. I would expect atleast it matches up with the max nodes possible on currently available systems. > >> Even >> with MAX_NUMNODES = 256, numa_distance is going to be just 64K. Hence there >> might not be much space to be saved that would need optimizing this path. >> Please correct me if I have missed something. > > Agreed. The saving is small. This was mostly about the code being misleading. > It gives the impression of doing dynamic sizing but doesn't actually do so as it > is using nr_node_ids before that value has been updated. I would prefer > to make the code 'obviously' correct. The x86 path is one approach, simply > hard coding the size as a constant is another. > > The secondary advantage would be to make it easy to unify this code across > architectures. Kind of inevitable riscv will be here soon and it would be nice > not to have a third slight variation on the code. I'd like to explore such > possible unification but it wasn't the main aim of this patch. There is already a RISC-V proposal in this regard which is trying to create a generic NUMA framework selectable with GENERIC_ARCH_NUMA. If the ultimate goal is unify the NUMA init path, we should try and see if that can also accommodate X86. https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=332897 > >> >>> >>> Note we could just decide to hardcode it as MAX_NUMNODES but if so we should >>> do so explicitly. >> >> nr_node_ids = MAX_NUMNODES which is set from mm/page_alloc.c, yes asserting >> with an WARN_ON() that it is indeed MAX_NUMNODES would make sense. > > OK, a WARN_ON would at least make it apparent this is a constant, not a dynamic > value as a reader of the code might assume (I did). > > Could we just go further and use MAX_NUMNODES directly and ignore nr_node_ids > for this purpose? IMHO this actually sounds better and cleaner. But the first preference should be to unify all these as GENERIC_ARCH_NUMA. > >> >>> >>> Looking at what x86 does, they do a walk of nodes_parsed and locally >>> establish the maximum node count seen. We can't actually do that where we >>> were previously calling it in numa_init because nodes_parsed isn't set up >>> either yet. So let us take a leaf entirely out of x86's book and make >>> the true assumption that nodes_parsed will definitely be set up before >>> we try to put a real value in this array. Hence just do it on demand. >> >> So it is replacing one assumption i.e nr_node_ids = MAX_NUMNODES with another >> i.e nodes_parsed has been initialized, while trying to populate an entry. > > Yes. If we make it clearly a fixed value, then I'm happy with that solution > to this particular problem. > > If not, I would argue that the use nodes_parsed makes it very much obvious that > we are assuming it was initialized. (Though on that argument we would have > assumed nr_node_ids had it's final value in the existing code and it doesn't, > I come back to my main argument being to make the code 'obviously' correct). > >> >>> >>> In order to avoid trying and failing to allocate the array multiple times >>> we do the same thing as x86 and set numa_distance = 1. This requires a >>> few small modifications elsewhere. >> >> Where ? Dont see numa_distance being set as 1. > > See below, I have highlighted the line. > >> >>> >>> Worth noting, that with one exception (which it appears can be removed [1]) >>> the x86 and arm numa distance code is now identical. Worth factoring it >>> out to some common location? >>> >>> [1] https://lkml.kernel.org/r/20170406124459.dwn5zhpr2xqg3lqm@xxxxxxxxxxxxxxxxxx >>> >>> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> >>> --- >>> arch/arm64/mm/numa.c | 35 ++++++++++++++++++----------------- >>> 1 file changed, 18 insertions(+), 17 deletions(-) >>> >>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c >>> index aafcee3e3f7e..a2f549ef0a36 100644 >>> --- a/arch/arm64/mm/numa.c >>> +++ b/arch/arm64/mm/numa.c >>> @@ -255,13 +255,11 @@ void __init numa_free_distance(void) >>> { >>> size_t size; >>> >>> - if (!numa_distance) >>> - return; >>> - >>> size = numa_distance_cnt * numa_distance_cnt * >>> sizeof(numa_distance[0]); >>> - >>> - memblock_free(__pa(numa_distance), size); >>> + /* numa_distance could be 1LU marking allocation failure, test cnt */ >>> + if (numa_distance_cnt) >>> + memblock_free(__pa(numa_distance), size); >>> numa_distance_cnt = 0; >>> numa_distance = NULL; >>> } >>> @@ -271,20 +269,29 @@ void __init numa_free_distance(void) >>> */ >>> static int __init numa_alloc_distance(void) >>> { >>> + nodemask_t nodes_parsed; >>> size_t size; >>> + int i, j, cnt = 0; >>> u64 phys; >>> - int i, j; >>> >>> - size = nr_node_ids * nr_node_ids * sizeof(numa_distance[0]); >>> + /* size the new table and allocate it */ >>> + nodes_parsed = numa_nodes_parsed; >>> + for_each_node_mask(i, nodes_parsed) >>> + cnt = i; >> >> There is no nodemask related helper to fetch the highest bit set ? > > Not that I can find. > > There is nodes_weight(), but I think we can currently end up with holes, > and it definitely isn't obvious from the local code that we can't. Right, the node mask can have holes, so nodes_weight() would not imply maximum possible node number. Possibly a new helper nodes_max() should do but not sure if there are any existing instances which could use such a helper. > > >> >>> + cnt++; >>> + size = cnt * cnt * sizeof(numa_distance[0]); >>> phys = memblock_find_in_range(0, PFN_PHYS(max_pfn), >>> size, PAGE_SIZE); >>> - if (WARN_ON(!phys)) >>> + if (!phys) { >>> + pr_warn("Warning: can't allocate distance table!\n"); >>> + /* don't retry until explicitly reset */ >>> + numa_distance = (void *)1LU; > > Here is where we set numa_distance to 1 in the error path. Got it. > >>> return -ENOMEM; >>> - >>> + } >>> memblock_reserve(phys, size); >>> >>> numa_distance = __va(phys); >>> - numa_distance_cnt = nr_node_ids; >>> + numa_distance_cnt = cnt; >>> >>> /* fill with the default distances */ >>> for (i = 0; i < numa_distance_cnt; i++) >>> @@ -311,10 +318,8 @@ static int __init numa_alloc_distance(void) >>> */ >>> void __init numa_set_distance(int from, int to, int distance) >>> { >>> - if (!numa_distance) { >>> - pr_warn_once("Warning: distance table not allocated yet\n"); >>> + if (!numa_distance && numa_alloc_distance() < 0) >>> return; >>> - } >>> >>> if (from >= numa_distance_cnt || to >= numa_distance_cnt || >>> from < 0 || to < 0) { >>> @@ -384,10 +389,6 @@ static int __init numa_init(int (*init_func)(void)) >>> nodes_clear(node_possible_map); >>> nodes_clear(node_online_map); >>> >>> - ret = numa_alloc_distance(); >>> - if (ret < 0) >>> - return ret; >>> - >>> ret = init_func(); >>> if (ret < 0) >>> goto out_free_distance; >>> >> >> What is the primary objective here ? Reduce memory for numa_distance[] >> or unifying arm64's numa_init() with that of x86's ? > > As mentioned above. The objective when I originally looked at this was > to make the code do what it appeared to do. The approach chosen was about > the added benefit of unifying this part with x86 + riscv etc. > Always good to not reinvent the wheel. Agreed.
