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: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: David Rowley <dgrowleyml@gmail.com>, 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: 2022-08-30T13:26:21Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> I guess the idea was to add a sentinel only when there already is space
> for it, but perhaps that's a bad tradeoff limiting the benefits. Either
> we add the sentinel fairly often (and then why not just add it all the
> time - it'll need a bit more space), or we do it only very rarely (and
> then it's a matter of luck if it catches an issue).

I'm fairly sure that when we made that decision originally, a top-of-mind
case was ListCells, which are plentiful, small, power-of-2-sized, and
not used in a way likely to have buffer overruns.  But since the List
rewrite a couple years back we no longer palloc individual ListCells.
So maybe we should revisit the question.  It'd be worth collecting some
stats about how much extra space would be needed if we force there
to be room for a sentinel.

			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