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    Subjectfast compressed fs (was Re: -nice tree)
    Hi!

    > > How?
    >
    > Run two parallel tasks: 1. write pages to disk by queuing the I/Os;
    > 2. compress unqueued pages.
    >
    > The first task won't use much CPU because it's always waiting for disk
    > DMAs to complete. While it sleeps, the second task runs.
    > Alternatively this can be implemented using polling for I/O
    > completions in the second task, if that's easier.
    >
    > The first task should keep the I/O queue full enough to sustain
    > writing, but not much fuller than that. Either a fixed queue length
    > will be fine, or it is easy to adjust the queue length dynamically by
    > enlarging it if any I/O completions occur when the queue is empty.
    >
    > The second task consumes uncompressed pages and makes available
    > compressed pages.
    >
    > When the first task wants to queue more pages for I/O, it first checks
    > the compressed-page list. If there are any, they are queued,
    > otherwise it consumes uncompressed pages.
    >
    > This will automatically converge on an optimal balance between
    > compressed and uncompressed page writing, provided the disk is using
    > DMA, which they do on all modern system.
    >
    > This is actually better than fully enabling or disabling compression.

    Very clever. This even could be used for a filesystem to make writes faster...
    Hmm, compressed fs and *faster* than normal... sounds good.

    --
    64 bytes from 195.113.31.123: icmp_seq=28 ttl=51 time=448769.1 ms

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