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    SubjectRe: [PATCH 1/3] blkdev: Submit discard bio in batches in blkdev_issue_discard()
    On Mon, 2 May 2011, Jens Axboe wrote:

    > On 2011-05-02 08:17, Lukas Czerner wrote:
    > > Currently we are waiting for every submitted REQ_DISCARD bio separately,
    > > but it can have unwanted consequences of repeatedly flushing the queue,
    > > so we rather submit bios in batches and wait for the entire batch, hence
    > > narrowing the window of other ios going in.
    > >
    > > Use bio_batch_end_io() and struct bio_batch for that purpose, the same
    > > is used by blkdev_issue_zeroout(). Also change bio_batch_end_io() so we
    > > always set !BIO_UPTODATE in the case of error and remove the check for
    > > bb, since we are the only user of this function and we always set this.
    > >
    > > Remove bio_get()/bio_put() from the blkdev_issue_discard() since
    > > bio_alloc() and bio_batch_end_io() is doing the same thing, hence it is
    > > not needed anymore.
    > >
    > > I have done simple dd testing with surprising results. The script I have
    > > used is:
    > >
    > > for i in $(seq 10); do
    > > echo $i
    > > dd if=/dev/sdb1 of=/dev/sdc1 bs=4k &
    > > sleep 5
    > > done
    > > /usr/bin/time -f %e ./blkdiscard /dev/sdc1
    > >
    > > Running time of BLKDISCARD on the whole device:
    > > with patch without patch
    > > 0.95 15.58
    > >
    > > So we can see that in this artificial test the kernel with the patch
    > > applied is approx 16x faster in discarding the device.
    >
    > Good results. It'd be more efficient to add the vectored discard support
    > and use it for this too though, and it would get rid of the need to wait
    > on the batches since there'd be just one discard bio for the ranges.
    >

    I know that you and Christoph were working on adding support for
    vectored discard, but I do not know what is the status of it ?

    Thanks!
    -Lukas


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