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: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>, Julien Rouhaud <rjuju123@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-10-07T00:50:11Z
Lists: pgsql-hackers 
On Fri, 7 Oct 2022 at 12:35, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Which leaves me with the attached proposed wording.

No objections here.

With these comments I'd be using slot MCTX_UNUSED4_ID first, then I'd
probably be looking at MCTX_UNUSED5_ID after adjusting wipe_mem to do
something other than setting bytes to 0x7F. I'd then use
MCTX_UNUSED3_ID since that pattern is only used for larger chunks with
glibc (per your findings).  After that, I'd probably start looking
into making more than 3 bits available. If that wasn't possible, I'd
be using MCTX_UNUSED2_ID and at last resort MCTX_UNUSED1_ID.

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