Re: tracepoints in ext4 (and/or ext3?)

[Eric Sandeen <sandeen@redhat.com>]

Theodore Tso wrote:
> On Tue, Aug 12, 2008 at 08:19:54AM -0500, Jose R. Santos wrote:
>> Good idea, although Im not sure if ext[34] is the best place we should
>> start putting markers though.
> 
> I can think of ext3/4 specific markers that would be useful for people
> who are tuning our filesystems for performance.  This would include
> when we start and end tranactions, when we force a checkpoint, when we
> create and, extend, and finish using a handle in the jbd layer.

Yep this is the kind of thing I thought of at first ...

> In the ext4 itself, knowing when we are mapping delayed allocations
> would be useful, as well as when we freeze and unfreeze a filesystem
> (i.e., for snapshots).

I could imagine even things like when/where/how big each allocation is,
also maybe some things in the lookup paths...

We might even be able to ditch the mballoc history in favor of
tracepoints if desired?

-Eric

> There are a lot of other tracepoints that probably do make more sense
> to be put in the VFS layer, although on thing that would be *really*
> nice is some semantic sugar in Systemtap or in a Systemtap tapset so
> that we only trigger the tracepoints for a particular filesystem.
> 
>      	     	     	 	     	   - Ted