Re: EXPERIMENTAL: mmap-based memory context / allocator

On 15.2.2015 21:13, Andres Freund wrote:
> On 2015-02-15 21:07:13 +0100, Tomas Vondra wrote:
>
>> malloc() does that only for allocations over MAP_THRESHOLD, which
>> is 128kB by default. Vast majority of blocks we allocate are <=
>> 8kB, so mmap() almost never happens.
>
> The problem is that mmap() is, to my knowledge, noticeably more
> expensive than sbrk(). Especially with concurrent workloads. Which is
> why the malloc/libc authors chose to use sbrk ...

Any ideas how to simulate such workloads? None of the tests I've done
suggested such issue exists.

> IIRC glibc malloc also batches several allocation into mmap()ed
> areas after some time.

Maybe, there's certainly a lot of such optimizations in libc. But how do
you return memory to system in that case?

--
Tomas Vondra http://www.2ndQuadrant.com/
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