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    SubjectRe: [PATCH 3/6] compcache: TLSF Allocator interface
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    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@chello.nl> 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.

    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 :-)



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