linux-kernel - Re: [patch 8/9] LTTng instrumentation

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Date:	Tue, 24 Mar 2009 19:39:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	ltt-dev@...ts.casi.polymtl.ca, linux-mm@...ck.org,
	Dave Hansen <haveblue@...ibm.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Hideo AOKI <haoki@...hat.com>,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [patch 8/9] LTTng instrumentation - filemap


* Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> Index: linux-2.6-lttng/mm/filemap.c

> +DEFINE_TRACE(wait_on_page_start);
> +DEFINE_TRACE(wait_on_page_end);

These are extremely incomplete - to the level of being useless.

To understand the lifetime of the pagecache, the following basic 
events have to be observed and instrumented:

 - create a new page
 - fill in a new page
 - dirty a page [when we know this]
 - request writeout of a page
 - clean a page / complete writeout
 - free a page due to MM pressure
 - free a page due to truncation/delete

The following additional events are useful as well:

 - mmap a page to a user-space address
 - copy a page to a user-space address (read)
 - write to a page from a user-space address (write)
 - unmap a page from a user-space address
 - fault in a user-space mapped pagecache page

optional:
   - shmem attach/detach events
   - shmem map/unmap events
   - hugetlb map/unmap events

I'm sure i havent listed them all. Have a look at the function-graph 
tracer output to see what kind of basic events can happen to a 
pagecache page.

	Ingo
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