On Wed, Nov 30, 2011 at 01:57:43AM +0800, Andi Kleen wrote:

On Tue, Nov 29, 2011 at 09:09:03PM +0800, Wu Fengguang wrote:

quoted

Record the readahead pattern in ra->pattern and extend the ra_submit()
parameters, to be used by the next readahead tracing/stats patches.

I like this, could it be exported it a bit more formally in /proc for 
each file descriptor?

Something like this?

        $ cat /proc/self/fdinfo/2
        pos:    0
        flags:  0100002
+       ra_pattern:      initial
+       ra_size:         4

It may be some rapidly changing information, however in practical
should remain stable unless it's changing access pattern a lot.

I could imagine a monitoring tool that you run on a process that
tells you what pattern state the various file descriptors are in and how
large the window is. That would be similar to the tools for
monitoring network connections, which are extremly useful 
in practice.

Yeah, the simplest form may be

        watch "head /proc/self/fdinfo/*"

Thanks,
Fengguang

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