Re: VFS hot tracking: How to calculate data temperature?

[Dave Chinner <david@fromorbit.com>]

On Fri, Nov 02, 2012 at 01:10:48PM -0700, Darrick J. Wong wrote:
> On Fri, Nov 02, 2012 at 04:41:09PM +0800, Zheng Liu wrote:
> > On Fri, Nov 02, 2012 at 02:38:29PM +0800, Zhi Yong Wu wrote:
> > > Here also has another question.
> > > 
> > > How to save the file temperature among the umount to be able to
> > > preserve the file tempreture after reboot?
> > > 
> > > This above is the requirement from DB product.
> > > I thought that we can save file temperature in its inode struct, that
> > > is, add one new field in struct inode, then this info will be written
> > > to disk with inode.
> > > 
> > > Any comments or ideas are appreciated, thanks.
> > 
> > Hi Zhiyong,
> > 
> > I think that we might define a callback function.  If a filesystem wants
> > to save these data, it can implement a function to save them.  The
> > filesystem can decide whether adding it or not by themselves.
> > 
> > BTW, actually I don't really care about how to save these data because I
> > only want to observe which file is accessed in real time, which is very
> > useful for me to track a problem in our product system.
> 
> <shrug> I _think_ the vfs quota code simply asks the filesystem for a special
> inode where it save the quota data in whatever (FS-agnostic) format it wants.
> Have you considered something like that?

Doesn't make a lot of sense because the data is per-inode. Storing
it per-inode is the only way it can be efficiently stored and
indexed as it is accessed at the same time the inode is accessed.

Quota information, OTOH, is per user/group/project - they are shared
structures and have a completely different lookup and index
mechanism to per-inode data structures. Henc eI don't think that
the quota model would be a good fit for such data.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com