On 8/30/22 04:31, David Rowley wrote: > On Tue, 30 Aug 2022 at 13:55, Tom Lane <t...@sss.pgh.pa.us> wrote: >> I wonder if slab ought to artificially bump up such requests when >> MEMORY_CONTEXT_CHECKING is enabled, so there's room for a sentinel. >> I think it's okay for aset.c to not do that, because its power-of-2 >> behavior means there usually is room for a sentinel; but slab's >> policy makes it much more likely that there won't be. > > I think it's fairly likely that small allocations are a power of 2, > and I think most of our allocates are small, so I imagine that if we > didn't do that for aset.c, we'd miss out on most of the benefits. > Yeah. I think we have a fair number of "larger" allocations (once you get to ~100B it probably won't be a 2^N), but we may easily miss whole sections of allocations. I guess the idea was to add a sentinel only when there already is space for it, but perhaps that's a bad tradeoff limiting the benefits. Either we add the sentinel fairly often (and then why not just add it all the time - it'll need a bit more space), or we do it only very rarely (and then it's a matter of luck if it catches an issue). Considering we only do this with asserts, I doubt the extra bytes / CPU is a major issue, and a (more) reliable detection of issues seems worth it. But maybe I underestimate the costs. The only alternative seems to be valgrind, and that's way costlier, though. regards -- Tomas Vondra EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... Tomas Vondra
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... Tomas Vondra
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tomas Vondra
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tomas Vondra
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tomas Vondra
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley
- Re: Reducing the chunk header sizes on all memory context typ... Tom Lane
- Re: Reducing the chunk header sizes on all memory context typ... David Rowley