linux-kernel - Re: [PATCH] Add tracepoints to track pagecache transition

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Date:	Thu, 19 Feb 2009 09:21:31 -0500
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Atsushi Tsuji <a-tsuji@...jp.nec.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Jason Baron <jbaron@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Kazuto Miyoshi <miyoshi@...ux.bs1.fc.nec.co.jp>,
	rostedt@...dmis.org, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH] Add tracepoints to track pagecache transition

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

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