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: Robert Haas <robertmhaas@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-30T16:17:33Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> Here's a patch which adds a comment to MemoryContextMethodID to Robert's patch.

OK, but while looking at that I noticed the adjacent

#define MEMORY_CONTEXT_METHODID_MASK \
	UINT64CONST((1 << MEMORY_CONTEXT_METHODID_BITS) - 1)

I'm rather astonished that that compiles; UINT64CONST was only ever
meant to be applied to *literals*.  I think what it's expanding to
is

	((1 << MEMORY_CONTEXT_METHODID_BITS) - 1UL)

(or on some machines 1ULL) which only accidentally does approximately
what you want.  It'd be all right perhaps to write

	((UINT64CONST(1) << MEMORY_CONTEXT_METHODID_BITS) - 1)

but you might as well avoid the Postgres-ism and just write

	((uint64) ((1 << MEMORY_CONTEXT_METHODID_BITS) - 1))

Nobody's ever going to make MEMORY_CONTEXT_METHODID_BITS large
enough for the shift to overflow in int arithmetic.

			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