Re: [PATCH 3/6] compcache: TLSF Allocator interface

[Nitin Gupta]

On Tue, Mar 25, 2008 at 12:26 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>
> On Mon, 2008-03-24 at 23:04 +0530, Nitin Gupta wrote:
>  > On Mon, Mar 24, 2008 at 10:26 PM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>  > > On Mon, 2008-03-24 at 20:34 +0530, Nitin Gupta wrote:
>  > >  > Two Level Segregate Fit (TLSF) Allocator is used to allocate memory for
>  > >  > variable size compressed pages. Its fast and gives low fragmentation.
>  > >  > Following links give details on this allocator:
>  > >  >  - http://rtportal.upv.es/rtmalloc/files/tlsf_paper_spe_2007.pdf
>  > >  >  - http://code.google.com/p/compcache/wiki/TLSFAllocator
>  > >  >
>  > >  > This kernel port of TLSF (v2.3.2) introduces several changes but underlying
>  > >  > algorithm remains the same.
>  > >  >
>  > >  > Changelog TLSF v2.3.2 vs this kernel port
>  > >  >  - Pool now dynamically expands/shrinks.
>  > >  >    It is collection of contiguous memory regions.
>  > >  >  - Changes to pool create interface as a result of above change.
>  > >  >  - Collect and export stats (/proc/tlsfinfo)
>  > >  >  - Cleanups: kernel coding style, added comments, macros -> static inline, etc.
>  > >
>  > >  Can you explain why you need this allocator, why don't the current
>  > >  kernel allocators work for you?
>  > >
>  > >
>  >
>  > kmalloc() allocates one of pre-defined sizes (as defined in
>  > kmalloc_sizes.h). This will surely cause severe fragmentation with
>  > these variable sized compressed pages.
>  >
>  > Whereas, TLSF maintains very fine grained size lists. In all the
>  > workloads I tested, it showed <5% fragmentation. Also, its very simple
>  > as just ~700 LOC.
>
>  Yeah, it also suffers from a horrible coding style, can use excessive
>  amounts of vmalloc space, isn't hooked into the reclaim process as an
>  allocator should be and has a severe lack of per-cpu data making it a
>  pretty big bottleneck on anything with more than a few cores.
>
>  Now, it might be needed, might work better, and the scalability issue
>  might not be a problem when used for swap, but still, you don't treat
>  any of these points in your changelog.

Currently, this TLSF implementation is not scalable at all (and thats
why it depends on EMBEDDED).

>
>  FWIW, please split up the patches in a sane way. This series looks like
>  it wants to be 2 or 3 patches. The first introducing all of TLSF (this
>  split per file is horrible). The second doing all of the block device,
>  and a possible last doing documentation and such.
>
>  Also, how bad was kmalloc() compared to this TLSF, we need numbers :-)
>
>

Ok, I will get them and present here.

Thanks,
Nitin
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