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: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-01T01:06:09Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> You're probably right we'll notice the clobber cases due to corruption
> of the next chunk header. The annoying thing is having a corrupted
> header only tells you there's a corruption somewhere, but it may be hard
> to know which part of the code caused it.

Same's true of a sentinel, though.

> OTOH we have platforms where valgrind is either not supported or no one
> runs tests with (e.g. on rpi4 it'd take insane amounts of code).

According to
https://valgrind.org/info/platforms.html
valgrind supports a pretty respectable set of platforms.  It might
be too slow to be useful on ancient hardware, of course.

I've had some success in identifying clobber perpetrators by putting
a hardware watchpoint on the clobbered word, which IIRC does work on
recent ARM hardware.  It's tedious and far more manual than valgrind,
but it's possible.

			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