[Tarantool-patches] [PATCH] small: unite the oscillation cache of all mempools
Konstantin Osipov
kostja.osipov at gmail.com
Thu Jan 30 00:46:03 MSK 2020
* Kirill Yukhin <kyukhin at tarantool.org> [20/01/29 13:30]:
> On 29 янв 04:48, Maksim Kulis wrote:
> > The task is to unite the oscillation cache of all mempools.
> > In the function slab_put_with_order() we check if there is any
> > slab of the largest size except the current one, in order to
> > avoid oscillation.
> > https://github.com/tarantool/small/blob/master/small/slab_cache.c#L349
>
> Thanks a lot for your patch. Since the change is performance
> related, before we start off review process, please provide a
> testcase (for tarantool or whatever) which will clearly show
> that there're cases where performance is actually increased.
>
> We won't accept "nice looking" perf patches.
It's not about performance :)
The patch reduces memory fragmentation quite a bit on small-arena
systems. Imagine a 1G system with slab_alloc_factor =1.06
(default). It can easily have up to 50-100 mempools in slab arena,
each holding up one mslab, up to 100-400MB in total.
The whole point of holding up to such mslab is to avoid mmap()
system call (which is costly) in cases like
for (i = 1..10000)
mslab_alloc()
mslab_free()
This is allocation scenario is called "oscilation".
There is no point in it, because there is already a cached mslab in
slab_cache, and it will be used just fine.
Maksim should update the CS comment.
--
Konstantin Osipov, Moscow, Russia
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