On Wed, Jul 28, 2021 at 02:47:23PM +0200, Michal Hocko wrote:

On Mon 12-07-21 16:09:33, Feng Tang wrote:

quoted

From: Ben Widawsky <redacted>

Adds a new mode to the existing mempolicy modes, MPOL_PREFERRED_MANY.

MPOL_PREFERRED_MANY will be adequately documented in the internal
admin-guide with this patch. Eventually, the man pages for mbind(2),
get_mempolicy(2), set_mempolicy(2) and numactl(8) will also have text
about this mode. Those shall contain the canonical reference.

NUMA systems continue to become more prevalent. New technologies like
PMEM make finer grain control over memory access patterns increasingly
desirable. MPOL_PREFERRED_MANY allows userspace to specify a set of
nodes that will be tried first when performing allocations. If those
allocations fail, all remaining nodes will be tried. It's a straight
forward API which solves many of the presumptive needs of system
administrators wanting to optimize workloads on such machines. The mode
will work either per VMA, or per thread.

Link: https://lore.kernel.org/r/20200630212517.308045-13-ben.widawsky@intel.com (local)
Signed-off-by: Ben Widawsky <redacted>
Signed-off-by: Feng Tang <redacted>
---
 Documentation/admin-guide/mm/numa_memory_policy.rst | 16 ++++++++++++----
 mm/mempolicy.c                                      |  7 +------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 067a90a1499c..cd653561e531 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst

@@ -245,6 +245,14 @@ MPOL_INTERLEAVED
 	address range or file.  During system boot up, the temporary
 	interleaved system default policy works in this mode.
 
+MPOL_PREFERRED_MANY
+        This mode specifies that the allocation should be attempted from the
+        nodemask specified in the policy. If that allocation fails, the kernel
+        will search other nodes, in order of increasing distance from the first
+        set bit in the nodemask based on information provided by the platform
+        firmware. It is similar to MPOL_PREFERRED with the main exception that
+        is an error to have an empty nodemask.

I believe the target audience of this documents are users rather than
kernel developers and for those the wording might be rather cryptic. I
would rephrase like this
	This mode specifices that the allocation should be preferrably
	satisfied from the nodemask specified in the policy. If there is
	a memory pressure on all nodes in the nodemask the allocation
	can fall back to all existing numa nodes. This is effectively
	MPOL_PREFERRED allowed for a mask rather than a single node.

With that or similar feel free to add
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

Will revise the test as suggested.

- Feng

-- 
Michal Hocko
SUSE Labs