Re: [PATCH] Add tracepoints to track pagecache transition

Lee Schermerhorn
2009-02-19T14:21:41Z

On Thu, 2009-02-19 at 22:12 +0900, KOSAKI Motohiro wrote:
> > Hi Kosaki-san,
> >
> > Thank you for your comment.
> >
> > KOSAKI Motohiro wrote:
> >> Hi
> >>
> >>
> >> In my 1st impression, this patch description is a bit strange.
> >>
> >>> The below patch adds instrumentation for pagecache.
> >>>
> >>> I thought it would be useful to trace pagecache behavior for problem
> >>> analysis (performance bottlenecks, behavior differences between stable
> >>> time and trouble time).
> >>>
> >>> By using those tracepoints, we can describe and visualize pagecache
> >>> transition (file-by-file basis) in kernel and pagecache
> >>> consumes most of the memory in running system and pagecache hit rate
> >>> and writeback behavior will influence system load and performance.
> >>
> >> Why do you think this tracepoint describe pagecache hit rate?
> >> and, why describe writeback behavior?
> >
> > I mean, we can describe file-by-file basis pagecache usage by using
> > these tracepoints and it is important for analyzing process I/O behavior.
>
> More confusing.
> Your page cache tracepoint don't have any per-process information.
>
>
> > Currently, we can understand the amount of pagecache from "Cached"
> > in /proc/meminfo. So I'd like to understand which files are using pagecache.
>
> There is one meta question, Why do you think file-by-file pagecache
> infomartion is valueable?
>

One might take a look at Marcello Tosatti's old 'vmtrace' patch. It
contains it's own data store/transport via relayfs, but the trace points
could be ported to the current kernel tracing infrastructure.

Here's a starting point: http://linux-mm.org/VmTrace

Quoting from that page:

>From the previous email to linux-mm:
>"The sequence of pages which a given process or workload accesses
>during its lifetime, a.k.a. "reference trace", is very important
>information. It has been used in the past for comparison of page
>replacement algorithms and other optimizations..."

Lee