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SubjectRe: [PATCH v6 5/6] mm/mempolicy: Advertise new MPOL_PREFERRED_MANY
On Wed, Jul 28, 2021 at 02:47:23PM +0200, Michal Hocko wrote:
> On Mon 12-07-21 16:09:33, Feng Tang wrote:
> > From: Ben Widawsky <ben.widawsky@intel.com>
> >
> > 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
> > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > Signed-off-by: Feng Tang <feng.tang@intel.com>
> > ---
> > 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

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