Re: scsi: fix sense_slab/bio swapping livelock - Kernel

This is a discussion on Re: scsi: fix sense_slab/bio swapping livelock - Kernel ; On Mon, Apr 07 2008 at 12:52 +0300, Pekka J Enberg wrote: > Hi Boaz, > > On Mon, 7 Apr 2008, Boaz Harrosh wrote: >> The slub behavior described above is disturbing. If I want a 128-byte kmalloc I ...

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Thread: Re: scsi: fix sense_slab/bio swapping livelock

  1. Re: scsi: fix sense_slab/bio swapping livelock

    On Mon, Apr 07 2008 at 12:52 +0300, Pekka J Enberg wrote:
    > Hi Boaz,
    >
    > On Mon, 7 Apr 2008, Boaz Harrosh wrote:
    >> The slub behavior described above is disturbing. If I want a 128-byte kmalloc I
    >> would use kmalloc. But if I want a dedicated kmem_cache of my own I take the trouble
    >> to create one. As I understood it, a dedicated kmem_cache is somewhat growing but
    >> lazy-shrinking and eventually maxes out to my usage of it. If I reserve one elemnt then
    >> even when memory is low and caches are shrunk I have at least a page. But more then
    >> In low memory condition, in a steady sate the cost of each allocation is kept low
    >> because I have the pages for my self and I don't need to go grabbing global locks.
    >> Sharing with other pools breaks that behavior. Perhaps we need a flag in kmem_cache
    >> creation that says we do not want slab sharing (OK slub sharing in this case).

    >
    > I think you're better off using the page allocator then. SLOB, for
    > example, doesn't guarantee you're the only user of a page for
    > kmem_cache_alloc() either and I don't really see why it should as it tries
    > to be as memory efficient as possible.
    >
    > Pekka


    Please forgive my ignorance, but what is then the difference between kmem_cache_alloc()
    and kmalloc?

    would you not agree that sometimes we want to override that sharing of SLOBs?

    Boaz
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  2. Re: scsi: fix sense_slab/bio swapping livelock

    Hi Boaz,

    On Mon, Apr 7, 2008 at 1:07 PM, Boaz Harrosh wrote:
    > Please forgive my ignorance, but what is then the difference between kmem_cache_alloc()
    > and kmalloc?


    Constructors, user-defined alignment, and tighter object packing.

    On Mon, Apr 7, 2008 at 1:07 PM, Boaz Harrosh wrote:
    > would you not agree that sometimes we want to override that sharing of SLOBs?


    To be honest, I really don't quite understand your use-case. But as
    far as I can tell, it hasn't never been explicitly guaranteed and most
    certainly has not been true since the merging of SLOB and more
    recently SLUB.

    Pekka
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