From mboxrd@z Thu Jan  1 00:00:00 1970
From: mingo@elte.hu (Ingo Molnar)
Date: Tue, 24 Mar 2009 19:39:40 +0100
Subject: [ltt-dev] [patch 8/9] LTTng instrumentation - filemap
In-Reply-To: <20090324160149.029092843@polymtl.ca>
References: <20090324155625.420966314@polymtl.ca>
	<20090324160149.029092843@polymtl.ca>
Message-ID: <20090324183940.GI31117@elte.hu>


* Mathieu Desnoyers <mathieu.desnoyers at polymtl.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