Hi Aneesh, On Wed, Oct 20, 2021 at 02:54:52PM +0530, Aneesh Kumar K.V wrote: > This syscall can be used to set a home node for the MPOL_BIND > and MPOL_PREFERRED_MANY memory policy. Users should use this > syscall after setting up a memory policy for the specified range > as shown below. > > mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp, > new_nodes->size + 1, 0); > sys_set_mempolicy_home_node((unsigned long)p, nr_pages * page_size, > home_node, 0); > > The syscall allows specifying a home node/preferred node from which kernel > will fulfill memory allocation requests first. > > For address range with MPOL_BIND memory policy, if nodemask specifies more > than one node, page allocations will come from the node in the nodemask > with sufficient free memory that is closest to the home node/preferred node. > > For MPOL_PREFERRED_MANY if the nodemask specifies more than one node, > page allocation will come from the node in the nodemask with sufficient > free memory that is closest to the home node/preferred node. If there is > not enough memory in all the nodes specified in the nodemask, the allocation > will be attempted from the closest numa node to the home node in the system. I can understand the requirement for MPOL_BIND, and for MPOL_PREFERRED_MANY, it provides 3 levels of preference: home node --> preferred nodes --> all nodes Any real usage cases for this? For a platform which may have 3 types of memory (HBM, DRAM, PMEM), this may be useful. > This helps applications to hint at a memory allocation preference node > and fallback to _only_ a set of nodes if the memory is not available > on the preferred node. Fallback allocation is attempted from the node which is > nearest to the preferred node. > > This helps applications to have control on memory allocation numa nodes and > avoids default fallback to slow memory NUMA nodes. For example a system with > NUMA nodes 1,2 and 3 with DRAM memory and 10, 11 and 12 of slow memory > > new_nodes = numa_bitmask_alloc(nr_nodes); > > numa_bitmask_setbit(new_nodes, 1); > numa_bitmask_setbit(new_nodes, 2); > numa_bitmask_setbit(new_nodes, 3); > > p = mmap(NULL, nr_pages * page_size, protflag, mapflag, -1, 0); > mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp, new_nodes->size + 1, 0); > > sys_set_mempolicy_home_node(p, nr_pages * page_size, 2, 0); For this example, it's 'mbind + sys_set_mempolicy_home_node', will case 'set_mempolicy + sys_set_mempolicy_home_node' be also supported? Thanks, Feng > This will allocate from nodes closer to node 2 and will make sure kernel will > only allocate from nodes 1, 2 and3. Memory will not be allocated from slow memory > nodes 10, 11 and 12 > > With MPOL_PREFERRED_MANY on the other hand will first try to allocate from the > closest node to node 2 from the node list 1, 2 and 3. If those nodes don't have > enough memory, kernel will allocate from slow memory node 10, 11 and 12 which > ever is closer to node 2. [SNIP]
