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Silence valgrind about pg_numa_touch_mem_if_required

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When querying NUMA status of pages in shared memory, we need to touch
the memory first to get valid results. This may trigger valgrind
reports, because some of the memory (e.g. unpinned buffers) may be
marked as noaccess.

Solved by adding a valgrind suppresion. An alternative would be to
adjust the access/noaccess status before touching the memory, but that
seems far too invasive. It would require all those places to have
detailed knowledge of what the shared memory stores.

The pg_numa_touch_mem_if_required() macro is replaced with a function.
Macros are invisible to suppressions, so it'd have to suppress reports
for the caller - e.g. pg_get_shmem_allocations_numa(). So we'd suppress
reports for the whole function, and that seems to heavy-handed. It might
easily hide other valid issues.

Reviewed-by: Christoph Berg <myon@debian.org>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/aEtDozLmtZddARdB@msg.df7cb.de
Backpatch-through: 18
This commit is contained in:
Tomas Vondra
2025-07-01 12:32:23 +02:00
parent 953050236a
commit 81f287dc92
4 changed files with 23 additions and 8 deletions
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3
contrib/pg_buffercache/pg_buffercache_pages.c
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@ -320,7 +320,6 @@ pg_buffercache_numa_pages(PG_FUNCTION_ARGS)
uint64 os_page_count;
int pages_per_buffer;
int max_entries;
volatile uint64 touch pg_attribute_unused();
char *startptr,
*endptr;
@ -375,7 +374,7 @@ pg_buffercache_numa_pages(PG_FUNCTION_ARGS)
/* Only need to touch memory once per backend process lifetime */
if (firstNumaTouch)
pg_numa_touch_mem_if_required(touch, ptr);
pg_numa_touch_mem_if_required(ptr);
}
Assert(idx == os_page_count);