mm/mempolicy: add set_mempolicy_home_node syscall

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.

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);

This will allocate from nodes closer to node 2 and will make sure the
kernel will only allocate from nodes 1, 2, and 3.  Memory will not be
allocated from slow memory nodes 10, 11, and 12.  This differs from
default MPOL_BIND behavior in that with default MPOL_BIND the allocation
will be attempted from node closer to the local node.  One of the
reasons to specify a home node is to allow allocations from cpu less
NUMA node and its nearby NUMA nodes.

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.

Link: https://lkml.kernel.org/r/20211202123810.267175-3-aneesh.kumar@linux.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 64fd0ba0d057..5a6afecbb0d0 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst
@@ -408,7 +408,7 @@ follows:
 Memory Policy APIs
 ==================
 
-Linux supports 3 system calls for controlling memory policy.  These APIS
+Linux supports 4 system calls for controlling memory policy.  These APIS
 always affect only the calling task, the calling task's address space, or
 some shared object mapped into the calling task's address space.
 
@@ -460,6 +460,20 @@ requested via the 'flags' argument.
 
 See the mbind(2) man page for more details.
 
+Set home node for a Range of Task's Address Spacec::
+
+	long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
+					 unsigned long home_node,
+					 unsigned long flags);
+
+sys_set_mempolicy_home_node set the home node for a VMA policy present in the
+task's address range. The system call updates the home node only for the existing
+mempolicy range. Other address ranges are ignored. A home node is the NUMA node
+closest to which page allocation will come from. Specifying the home node override
+the default allocation policy to allocate memory close to the local node for an
+executing CPU.
+
+
 Memory Policy Command Line Interface
 ====================================