Horton

Re: Reducing the chunk header sizes on all memory context types

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-29T13:47:43Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> I suspect, going by all 3 failing animals being 32-bit which have a
> MAXIMUM_ALIGNOF 8 and SIZEOF_SIZE_T of 4 that this is due to the lack
> of padding in the MemoryChunk struct.
> AllocChunkData and GenerationChunk had padding to account for
> sizeof(Size) being 4 and sizeof(void *) being 8, I didn't add that to
> MemoryChunk, so I'll do that now.

Doesn't seem to have fixed it.  IMO, the fact that we can get through
core regression tests and pg_upgrade is a strong indicator that
there's not anything fundamentally wrong with memory context
management.  I'm inclined to think the problem is in d2169c9985,
instead ... though I can't see anything wrong with it.

Another possibility is that there's a pre-existing bug in the
logical decoding stuff that your changes accidentally exposed.
I wonder if valgrind would show anything interesting.

			regards, tom lane

Commits

  1. Harden memory context allocators against bogus chunk pointers.

  2. Improve our ability to detect bogus pointers passed to pfree et al.

  3. Remove MemoryContextContains().

  4. Remove uses of MemoryContextContains in nodeAgg.c and nodeWindowAgg.c.

  5. Temporarily make MemoryContextContains return false

  6. Make MemoryContextContains work correctly again

  7. Make more effort to put a sentinel at the end of allocated memory

  8. Fix some possibly latent bugs in slab.c

  9. Various cleanups of the new memory context header code

  10. Revert "Add missing padding from MemoryChunk struct"

  11. Use MAXALIGN() in calculations using sizeof(SlabBlock)

  12. Add missing padding from MemoryChunk struct

  13. Improve performance of and reduce overheads of memory management