On Mon 12-07-21 16:09:33, Feng Tang wrote: > From: Ben Widawsky <ben.widawsky@xxxxxxxxx> > > 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@xxxxxxxxx > Signed-off-by: Ben Widawsky <ben.widawsky@xxxxxxxxx> > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > --- > 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@xxxxxxxx> -- Michal Hocko SUSE Labs
