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>, Julien Rouhaud <rjuju123@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-10-10T21:07:53Z
Lists: pgsql-hackers 
David Rowley <dgrowleyml@gmail.com> writes:
> Looking at your changes to SlabFree(), I don't really think that
> change is well aligned to the newly proposed policy. My understanding
> of the rationale behind this policy is that large chunks get malloced
> and will be slower anyway, so the elog(ERROR) is less overhead for
> those.  In SlabFree(), we're most likely not doing any free()s, so I
> don't quite understand why you've added the elog rather than the
> Assert for this case. The slab allocator *should* be very fast.

Yeah, slab.c hasn't any distinction between large and small chunks,
so we have to just pick one policy or the other.  I'd hoped to get
away with the more robust runtime test on the basis that slab allocation
is not used so much that this'd result in any noticeable performance
change.  SlabRealloc, at least, is not used *at all* per the code
coverage tests, and if we're there at all we should be highly suspicious
that something is wrong.  However, I could be wrong about SlabFree,
and if you're going to hold my feet to the fire then I'll change it
rather than try to produce some performance evidence.

			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