Re: [PATCH 3/3] slub: build detached freelist with look-ahead

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Wed, Jul 22, 2015 at 01:28:19AM +0200, Jesper Dangaard Brouer wrote:
> On Tue, 21 Jul 2015 08:50:36 -0500 (CDT)
> Christoph Lameter <cl@linux.com> wrote:
> 
> > On Mon, 20 Jul 2015, Jesper Dangaard Brouer wrote:
> > 
> > > Yes, I think it is merged... how do I turn off merging?
> > 
> > linux/Documentation/kernel-parameters.txt
> > 
> >         slab_nomerge    [MM]
> >                         Disable merging of slabs with similar size. May be
> >                         necessary if there is some reason to distinguish
> >                         allocs to different slabs. Debug options disable
> >                         merging on their own.
> >                         For more information see Documentation/vm/slub.txt.
> 
> I was hoping I could define this per slub runtime.  Any chance this
> would be made possible?

It's not possible to set/reset slab merge in runtime. Once merging
happens, one slab could have objects from different kmem_caches so we
can't separate it cleanly. Current best approach is to prevent merging
when creating new kmem_cache by introducing new slab flag
like as SLAB_NO_MERGE.

> 
> Setting boot param "slab_nomerge" made my benchmarking VERY stable
> between runs (obj size 256).
> 
> 
> Run01: slab_nomerge
> 1 - 63 cycles(tsc) 15.927 ns -  46 cycles(tsc) 11.707 ns
> 2 - 56 cycles(tsc) 14.185 ns -  28 cycles(tsc) 7.129 ns
> 3 - 54 cycles(tsc) 13.588 ns -  23 cycles(tsc) 5.762 ns
> 4 - 53 cycles(tsc) 13.291 ns -  20 cycles(tsc) 5.085 ns
> 8 - 51 cycles(tsc) 12.918 ns -  19 cycles(tsc) 4.886 ns
> 16 - 50 cycles(tsc) 12.607 ns -  19 cycles(tsc) 4.858 ns
> 30 - 51 cycles(tsc) 12.759 ns -  19 cycles(tsc) 4.980 ns
> 32 - 51 cycles(tsc) 12.930 ns -  19 cycles(tsc) 4.975 ns
> 34 - 93 cycles(tsc) 23.410 ns -  27 cycles(tsc) 6.924 ns
> 48 - 80 cycles(tsc) 20.193 ns -  25 cycles(tsc) 6.279 ns
> 64 - 73 cycles(tsc) 18.322 ns -  23 cycles(tsc) 5.939 ns
> 128 - 88 cycles(tsc) 22.083 ns -  29 cycles(tsc) 7.413 ns
> 158 - 97 cycles(tsc) 24.274 ns -  34 cycles(tsc) 8.696 ns
> 250 - 102 cycles(tsc) 25.556 ns -  40 cycles(tsc) 10.100 ns
> 
> Run02: slab_nomerge
> 1 - 63 cycles(tsc) 15.879 ns -  46 cycles(tsc) 11.701 ns
> 2 - 56 cycles(tsc) 14.222 ns -  28 cycles(tsc) 7.140 ns
> 3 - 54 cycles(tsc) 13.586 ns -  23 cycles(tsc) 5.783 ns
> 4 - 53 cycles(tsc) 13.339 ns -  20 cycles(tsc) 5.095 ns
> 8 - 51 cycles(tsc) 12.899 ns -  19 cycles(tsc) 4.905 ns
> 16 - 50 cycles(tsc) 12.624 ns -  19 cycles(tsc) 4.853 ns
> 30 - 51 cycles(tsc) 12.781 ns -  19 cycles(tsc) 4.984 ns
> 32 - 51 cycles(tsc) 12.933 ns -  19 cycles(tsc) 4.997 ns
> 34 - 93 cycles(tsc) 23.421 ns -  27 cycles(tsc) 6.909 ns
> 48 - 80 cycles(tsc) 20.241 ns -  25 cycles(tsc) 6.267 ns
> 64 - 73 cycles(tsc) 18.346 ns -  23 cycles(tsc) 5.947 ns
> 128 - 88 cycles(tsc) 22.192 ns -  29 cycles(tsc) 7.415 ns
> 158 - 97 cycles(tsc) 24.358 ns -  34 cycles(tsc) 8.693 ns
> 250 - 102 cycles(tsc) 25.597 ns -  40 cycles(tsc) 10.144 ns
> 
> Run03: slab_nomerge
> 1 - 63 cycles(tsc) 15.897 ns -  46 cycles(tsc) 11.685 ns
> 2 - 56 cycles(tsc) 14.178 ns -  28 cycles(tsc) 7.132 ns
> 3 - 54 cycles(tsc) 13.590 ns -  23 cycles(tsc) 5.774 ns
> 4 - 53 cycles(tsc) 13.314 ns -  20 cycles(tsc) 5.092 ns
> 8 - 51 cycles(tsc) 12.872 ns -  19 cycles(tsc) 4.886 ns
> 16 - 50 cycles(tsc) 12.603 ns -  19 cycles(tsc) 4.840 ns
> 30 - 50 cycles(tsc) 12.750 ns -  19 cycles(tsc) 4.966 ns
> 32 - 51 cycles(tsc) 12.910 ns -  19 cycles(tsc) 4.977 ns
> 34 - 93 cycles(tsc) 23.372 ns -  27 cycles(tsc) 6.929 ns
> 48 - 80 cycles(tsc) 20.205 ns -  25 cycles(tsc) 6.276 ns
> 64 - 73 cycles(tsc) 18.292 ns -  23 cycles(tsc) 5.929 ns
> 128 - 90 cycles(tsc) 22.516 ns -  29 cycles(tsc) 7.425 ns
> 158 - 99 cycles(tsc) 24.825 ns -  34 cycles(tsc) 8.668 ns
> 250 - 102 cycles(tsc) 25.652 ns -  40 cycles(tsc) 10.129 ns

Really looks stable!

Thanks.

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