pgsql: Handle EPERM in pg_numa_init

Handle EPERM in pg_numa_init

When running in Docker, the container may not have privileges needed by
get_mempolicy(). This is called by numa_available() in libnuma, but
versions prior to 2.0.19 did not expect that. The numa_available() call
seemingly succeeds, but then we get unexpected failures when trying to
query status of pages:

postgres =# select * from pg_shmem_allocations_numa;
ERROR: XX000: failed NUMA pages inquiry status: Operation not
permitted
LOCATION: pg_get_shmem_allocations_numa, shmem.c:691

The best solution is to call get_mempolicy() first, and proceed to
numa_available() only when it does not fail with EPERM. Otherwise we'd
need to treat older libnuma versions as insufficient, which seems a bit
too harsh, as this only affects containerized systems.

Fix by me, based on suggestions by Christoph. Backpatch to 18, where the
NUMA functions were introduced.

Reported-by: Christoph Berg <myon(at)debian(dot)org>
Reviewed-by: Christoph Berg <myon(at)debian(dot)org>
Discussion: https://postgr.es/m/aPDZOxjrmEo_1JRG@msg.df7cb.de
Backpatch-through: 18

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/482e98ac43022194fbf2ef0d8f6a68fe2516e54a

Modified Files
--------------
src/port/pg_numa.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)