pgsql: Make after-startup shmem failure test reliable

Make after-startup shmem failure test reliable

The test expects a 128 kB request to exceed the shared memory available after
startup. Huge pages can round up the main shared memory segment enough for
that request to succeed, defeating the test.

Disable huge pages for the allocation-failure phase so that it exercises the
intended error path independently of shared memory segment rounding.

Author: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reported-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/rpkhzrrmo7qiz7rr3qlufksb2oci33wcg3ao75le7dqindgoif@6yozkjwb6bdf
Backpatch-through: 19

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e916927cfbc0e6aed4dfe0d6018c42abc7fc493c

Modified Files
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src/test/modules/test_shmem/t/001_late_shmem_alloc.pl | 3 +++
1 file changed, 3 insertions(+)