linux-kernel - Re: [rfc][patch] SLQB slab allocator

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Date:	Wed, 17 Dec 2008 08:09:54 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	MinChan Kim <minchan.kim@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [rfc][patch] SLQB slab allocator

On Wed, Dec 17, 2008 at 04:01:06PM +0900, MinChan Kim wrote:
> On Wed, Dec 17, 2008 at 3:42 PM, Nick Piggin <npiggin@...e.de> wrote:
> >> Below is average for ten time test.
> >>
> >> slab :
> >> user : 2376.484, system : 192.616 elapsed : 12:22.0
> >> slub :
> >> user : 2378.439, system : 194.989 elapsed : 12:22.4
> >> slqb :
> >> user : 2380.556, system : 194.801 elapsed : 12:23.0
> >>
> >> so, slqb is rather slow although it is a big difference.
> >> Interestingly, slqb consumes less time than slub in system.
> >
> > Thanks, interesting test. kbuild is not very slab allocator intensive,
> 
> Let me know what is popular benchmark program in slab allocator.
> I will try with it. :)

That's not to say it is a bad benchmark :) If it shows up a difference
and is a useful workload like kbuild, then it is a good benchmark.

Allocator changes tend to show up more when there is a lot of network
or disk IO happening. But it is good to see other tets too, so any
numbers you get are welcome.

> > so I hadn't thought of trying it. Possibly the object cacheline layout
> > of longer lived allocations changes the behaviour (increased user time
> > could indicate that).
> 
> What mean "object cacheline layout of loger lived allocations" ?

For example, different allocation schemes will alter the chances of
getting different ways (colours), or false sharing. SLUB and SLQB
for example allow as fine as 8 byte allocation granularity wheras
SLAB goes down to 32 bytes, so small objects *could* be more prone
to false sharing. I don't know for sure at this stage, just guessing ;)

The difference doesn't show up significantly on my system, so profiling
doesn't reveal anything (I guess even on your system it would be
difficult to profile because it is not a huge difference).

> > I've been making a few changes to that, and hopefully slqb is slightly
> > improved now (the margin is much closer, seems within the noise with
> > SLUB on my NUMA opteron now, although that's a very different system).
> >
> > The biggest bug I fixed was that the NUMA path wasn't being taken in
> > kmem_cache_free on NUMA systems (oops), but that wouldn't change your
> > result. But I did make some other changes too, eg in prefetching.
> 
> OK. I will review and test your new patch in my machine.

Thanks! Code style and comments should be improved quite a bit now.

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