| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Reducing the chunk header sizes on all memory context types |
| Date: | 2022-08-29 15:43:14 |
| Message-ID: | 3209705.1661787794@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
> I suspect it's a pre-existing bug in Slab allocator, because it does this:
> #define SlabBlockGetChunk(slab, block, idx) \
> ((MemoryChunk *) ((char *) (block) + sizeof(SlabBlock) \
> + (idx * slab->fullChunkSize)))
> and SlabBlock is only 20B, i.e. not a multiple of 8B. Which would mean
> that even if we allocate block and size the chunks carefully (with all
> the MAXALIGN things), we ultimately slice the block incorrectly.
Right, same conclusion I just came to. But it's not a "pre-existing"
bug, because sizeof(SlabBlock) *was* maxaligned until David added
another field to it.
I think adding a padding field to SlabBlock would be a less messy
solution than your patch.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Magnus Hagander | 2022-08-29 15:44:25 | Re: wal_sync_method=fsync_writethrough |
| Previous Message | Tomas Vondra | 2022-08-29 15:39:52 | Re: Reducing the chunk header sizes on all memory context types |