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    SubjectRe: cleancache can lead to serious performance degradation
    On 08/25/2011 11:56 AM, Dan Magenheimer wrote:

    > Third, zcache is relatively new and can certainly benefit from
    > the input of other developers. The lzo1x compression in the kernel
    > is fairly slow; Seth Jennings (cc'ed) is looking into alternate
    > compression technologies. Perhaps there is a better compression
    > choice more suitable for older-slower processors, probably with a
    > poorer compression ratio. Further, zcache currently does compression
    > and decompression with interrupts disabled, which may be a
    > significant factor in the slowdowns you've observed. This should
    > be fixable.

    This was something I've meaning to ask about. Why are compression
    and decompression done with interrupts disabled? What would need
    to change so that we don't have to disable interrupts?

    >>> I guess that possible workaround could be to implement some kind of
    >>> compression throttling valve for cleancache/zcache:
    >>> - if there's available CPU time (idle cycles or so), then compress
    >>> (maybe even with low CPU scheduler priority);
    > Agreed, and this low-priority kernel thread ideally would also
    > solve the "compress while irqs disabled" problem!


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