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: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-06T02:43:14Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> I think the fix is harder than I thought, or perhaps impossible to do
> given how we now determine the owning MemoryContext of a pointer.

> There's a comment in MemoryContextContains which says:

> * NB: Can't use GetMemoryChunkContext() here - that performs assertions
> * that aren't acceptable here since we might be passed memory not
> * allocated by any memory context.

I think MemoryContextContains' charter is to return

	GetMemoryChunkContext(pointer) == context

*except* that instead of asserting what GetMemoryChunkContext asserts,
it should treat those cases as reasons to return false.  So if you
can still do GetMemoryChunkContext then you can still do
MemoryContextContains.  The point of having the separate function
is to be as forgiving as we can of bogus pointers.

			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