Horton

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

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, 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: 2022-08-30T02:29:01Z
Lists: pgsql-hackers 
On Tue, 30 Aug 2022 at 13:58, Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
> armv7l (32-bit rpi4)
>
> +WARNING:  chunkSize 216 fullChunkSize 232 header 16
> +WARNING:  chunkSize 64 fullChunkSize 80 header 16
>
> aarch64 (64-bit rpi4)
>
> +WARNING:  chunkSize 304 fullChunkSize 320 header 16
> +WARNING:  chunkSize 80 fullChunkSize 96 header 16
>
> So indeed, those are *perfect* matches and thus the sentinel_ok() never
> executed. So no failures until now. On x86-64 I get the same thing as on
> aarch64. I guess that explains why it never failed. Seems like a pretty
> amazing coincidence ...

hmm, I'm not so sure I agree that it's an amazing coincidence. Isn't
it quite likely that the chunksize being given to SlabContextCreate()
is the same as MAXALIGN(chunksize)? Isn't that all it would take?

David

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