Re: SlabCheck leaks memory into TopMemoryContext

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: SlabCheck leaks memory into TopMemoryContext
Date: 2020-01-16 16:48:49
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On 2020-01-16 17:25:00 +0100, Tomas Vondra wrote:
> On Thu, Jan 16, 2020 at 10:27:01AM -0500, Tom Lane wrote:
> > Andres Freund <andres(at)anarazel(dot)de> writes:
> > > ... I thought you were asking whether
> > > any additional memory could just be avoided...
> >
> > Well, I was kind of wondering that, but if it's not practical then
> > preallocating the space instead will do.
> >
> I don't think it's practical to rework the checks in a way that would
> not require allocations. Maybe it's possible, but I think it's not worth
> the extra complexity.
> The attached fix should do the trick - it pre-allocates the space when
> creating the context. There is a bit of complexity because we want to
> allocate the space as part of the context header, but nothin too bad. We
> might optimize it a bit by using a regular bitmap (instead of just an
> array of bools), but I haven't done that.

I don't get why it's advantageous to allocate this once for each slab,
rather than having it as a global once for all slabs. But anyway, still
clearly better than the current situation.

- Andres

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