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    SubjectRe: [PATCH 7/9] readahead: add vfs/readahead tracing event
    On Tue, Nov 29, 2011 at 11:22:28PM +0800, Jan Kara wrote:
    > On Tue 29-11-11 21:09:07, Wu Fengguang wrote:
    > > This is very useful for verifying whether the readahead algorithms are
    > > working to the expectation.
    > >
    > > Example output:
    > >
    > > # echo 1 > /debug/tracing/events/vfs/readahead/enable
    > > # cp test-file /dev/null
    > > # cat /debug/tracing/trace # trimmed output
    > > readahead-initial(dev=0:15, ino=100177, req=0+2, ra=0+4-2, async=0) = 4
    > > readahead-subsequent(dev=0:15, ino=100177, req=2+2, ra=4+8-8, async=1) = 8
    > > readahead-subsequent(dev=0:15, ino=100177, req=4+2, ra=12+16-16, async=1) = 16
    > > readahead-subsequent(dev=0:15, ino=100177, req=12+2, ra=28+32-32, async=1) = 32
    > > readahead-subsequent(dev=0:15, ino=100177, req=28+2, ra=60+60-60, async=1) = 24
    > > readahead-subsequent(dev=0:15, ino=100177, req=60+2, ra=120+60-60, async=1) = 0
    > >
    > > CC: Ingo Molnar <mingo@elte.hu>
    > > CC: Jens Axboe <axboe@kernel.dk>
    > > CC: Steven Rostedt <rostedt@goodmis.org>
    > > CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > > Acked-by: Rik van Riel <riel@redhat.com>
    > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > Looks OK.
    >
    > Acked-by: Jan Kara <jack@suse.cz>

    Thank you.

    > > + TP_printk("readahead-%s(dev=%d:%d, ino=%lu, "
    > > + "req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d",
    > > + ra_pattern_names[__entry->pattern],
    > > + MAJOR(__entry->dev),
    > > + MINOR(__entry->dev),

    One thing I'm not certain is the dev=MAJOR:MINOR. The other option
    used in many trace events are bdi=BDI_NAME_OR_NUMBER. Will bdi be more
    suitable here?

    Thanks,
    Fengguang


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