Horton

Re: Reducing the chunk header sizes on all memory context types

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.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: 2022-09-01T00:31:58Z
Lists: pgsql-hackers 
On Thu, 1 Sept 2022 at 12:23, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Is there reason to think we can't validate headers enough to catch
> clobbers?

For non-sentinel chunks, the next byte after the end of the chunk will
be storing the block offset for the following chunk.  I think:

if (block != MemoryChunkGetBlock(chunk))
elog(WARNING, "problem in alloc set %s: bad block offset for chunk %p
in block %p",
name, chunk, block);

should catch those.

Maybe we should just consider always making room for a sentinel for
chunks that are on dedicated blocks. At most that's an extra 8 bytes
in some allocation that's either over 1024 or 8192 (depending on
maxBlockSize).

David

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