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    SubjectRe: [PATCH 2/3]: xvmalloc memory allocator
    Pekka Enberg wrote:
    > On Tue, 17 Mar 2009, Nitin Gupta wrote:
    >>> Creating slabs for sizes in range, say, [32, 3/4*PAGE_SIZE] separated by
    >>> 64bytes
    >>> will require 48 slabs! Then for slab of each size class will have wastage
    >>> due to
    >>> unused slab objects in each class.
    >>> Larger difference in slab sizes (and thus small no. of them), will surely
    >>> cause too much
    >>> wastage due to internal fragmentation.
    > On Tue, Mar 17, 2009 at 10:58 AM, Christoph Lameter
    > <> wrote:
    >> The slabs that match existing other slabs of similar sizes will be aliased
    >> and not created. Create the 48 slabs and you likely will only use 10 real
    >> additional ones. The rest will just be pointing to existing ones.
    > Yup. One thing I don't quite understand is why you need all the 48
    > caches in the first place. Allocation sizes tend to be clustered and I
    > would have imagined you'd see that when compressing page sized chunks
    > as well.

    Compressed page lengths sometimes do tend to cluster within somewhat
    small range. However, the range of where majority of pages will lie depends
    highly of workload - sometimes range is not clear and sometime there is no
    preferred range at all. Please refer this data:

    It shows compressed page size distribution for various workloads.

    > Using kmemtrace to analyze the exact reason for the bad
    > fragmentation would probably be helpful.

    That was purely internal fragmentation.
    Wastage per obj = ksize(obj) - actual_size.

    Code used for testing:
    This is a "SwapReplay client". Please see:


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