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: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, David Rowley <dgrowleyml@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-09T19:21:57Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> I think it's fine, given that we can change this at any time, but it's
> probably worth to explicitly agree that this will for now restrict us to 8
> context methods?

Do we really need it to be that tight?  I know we only have 3 methods today,
but 8 doesn't seem that far away.  If there were six bits reserved for
this I'd be happier.

>> # We also add a restriction that block sizes for all 3 of the memory
>> # allocators cannot be 1GB or larger.  We would be unable to store the
>> # number of bytes that the block is offset from the chunk stored beyond this
>> #1GB boundary on any block that was larger than 1GB.

Losing MemoryContextAllocHuge would be very bad, so I assume this comment
is not telling the full truth.

			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