On Mon, Mar 25, 2019 at 12:28 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote: > > > > On 3/23/19 10:21 AM, Dan Williams wrote: > > On Fri, Mar 22, 2019 at 9:45 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote: > >> When running applications on the machine with NVDIMM as NUMA node, the > >> memory allocation may end up on NVDIMM node. This may result in silent > >> performance degradation and regression due to the difference of hardware > >> property. > >> > >> DRAM first should be obeyed to prevent from surprising regression. Any > >> non-DRAM nodes should be excluded from default allocation. Use nodemask > >> to control the memory placement. Introduce def_alloc_nodemask which has > >> DRAM nodes set only. Any non-DRAM allocation should be specified by > >> NUMA policy explicitly. > >> > >> In the future we may be able to extract the memory charasteristics from > >> HMAT or other source to build up the default allocation nodemask. > >> However, just distinguish DRAM and PMEM (non-DRAM) nodes by SRAT flag > >> for the time being. > >> > >> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > >> --- > >> arch/x86/mm/numa.c | 1 + > >> drivers/acpi/numa.c | 8 ++++++++ > >> include/linux/mmzone.h | 3 +++ > >> mm/page_alloc.c | 18 ++++++++++++++++-- > >> 4 files changed, 28 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c > >> index dfb6c4d..d9e0ca4 100644 > >> --- a/arch/x86/mm/numa.c > >> +++ b/arch/x86/mm/numa.c > >> @@ -626,6 +626,7 @@ static int __init numa_init(int (*init_func)(void)) > >> nodes_clear(numa_nodes_parsed); > >> nodes_clear(node_possible_map); > >> nodes_clear(node_online_map); > >> + nodes_clear(def_alloc_nodemask); > >> memset(&numa_meminfo, 0, sizeof(numa_meminfo)); > >> WARN_ON(memblock_set_node(0, ULLONG_MAX, &memblock.memory, > >> MAX_NUMNODES)); > >> diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c > >> index 867f6e3..79dfedf 100644 > >> --- a/drivers/acpi/numa.c > >> +++ b/drivers/acpi/numa.c > >> @@ -296,6 +296,14 @@ void __init acpi_numa_slit_init(struct acpi_table_slit *slit) > >> goto out_err_bad_srat; > >> } > >> > >> + /* > >> + * Non volatile memory is excluded from zonelist by default. > >> + * Only regular DRAM nodes are set in default allocation node > >> + * mask. > >> + */ > >> + if (!(ma->flags & ACPI_SRAT_MEM_NON_VOLATILE)) > >> + node_set(node, def_alloc_nodemask); > > Hmm, no, I don't think we should do this. Especially considering > > current generation NVDIMMs are energy backed DRAM there is no > > performance difference that should be assumed by the non-volatile > > flag. > > Actually, here I would like to initialize a node mask for default > allocation. Memory allocation should not end up on any nodes excluded by > this node mask unless they are specified by mempolicy. > > We may have a few different ways or criteria to initialize the node > mask, for example, we can read from HMAT (when HMAT is ready in the > future), and we definitely could have non-DRAM nodes set if they have no > performance difference (I'm supposed you mean NVDIMM-F or HBM). > > As long as there are different tiers, distinguished by performance, for > main memory, IMHO, there should be a defined default allocation node > mask to control the memory placement no matter where we get the information. I understand the intent, but I don't think the kernel should have such a hardline policy by default. However, it would be worthwhile mechanism and policy to consider for the dax-hotplug userspace tooling. I.e. arrange for a given device-dax instance to be onlined, but set the policy to require explicit opt-in by numa binding for it to be an allocation / migration option. I added Vishal to the cc who is looking into such policy tooling. > But, for now we haven't had such information ready for such use yet, so > the SRAT flag might be a choice. > > > > > Why isn't default SLIT distance sufficient for ensuring a DRAM-first > > default policy? > > "DRAM-first" may sound ambiguous, actually I mean "DRAM only by > default". SLIT should just can tell us what node is local what node is > remote, but can't tell us the performance difference. I think it's a useful semantic, but let's leave the selection of that policy to an explicit userspace decision.
