Re: [RFC PATCH 0/5] Add accountings for Page Cache

[Liu Yuan <namei.unix@gmail.com>]

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On Thu, Mar 3, 2011 at 9:50 AM, KOSAKI Motohiro <
kosaki.motohiro@jp.fujitsu.com> wrote:

> > [Summery]
> >
> > In order to evaluate page cache efficiency, system admins are happy to
> > know whether a block of data is cached for subsequent use, or whether
> > the page is read-in but seldom used. This patch extends an effort to
> > provide such kind of information. We adds three counters, which are
> > exported to the user space, for the Page Cache that is almost
> > transparent to the applications. This would benifit some heavy page
> > cache users that might try to tune the performance in hybrid storage
> > situation.
>
> I think you need to explain exact and concrete use-case. Typically,
> cache-hit ratio doesn't help administrator at all. because merely backup
> operation (eg. cp, dd, et al) makes prenty cache-miss. But it is no sign
> of memory shortage. Usually, vmscan stastics may help memroy utilization
> obzavation.
>
> Plus, as ingo said, you have to consider to use trancepoint framework
> at first. Because, it is zero cost if an admin don't enable such
> tracepoint.
>
>
Thanks very much for your comments.

Yeah, we'er going to try tracepoint and perf as Ingo said.


> At last, I don't think disk_stats have to have page cache stastics. It
> seems
> slightly layer violation.
>
> Thanks.
>
>
This is the starting point of the patch set, so I simply embedded the
structure into the existing infrastructure. This did saved me a lot of
effort because disk_stats is a good place to collect stats on _partition_
basis. Anyway, as you pointed out, this is kind of the mess.

Thanks,
Yuan

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