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

[Ram Pai <linuxram@us.ibm.com>]

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.

To me, umounting a filesystem is a way of explicitly telling the VFS that the
filesystem's data is not hot anymore. So probably, it really does not make
sense to store temperatures across mount boundaries.

RP