On 04/19/2012 09:20 PM, Theodore Ts'o wrote:

As I had brought up during one of the lightning talks at the Linux
Storage and Filesystem workshop, I am interested in introducing two new
open flags, O_HOT and O_COLD.  These flags are passed down to the
individual file system's inode operations' create function, and the file
system can use these flags as a hint regarding whether the file is
likely to be accessed frequently or not.

In the future I plan to do further work on how ext4 would use these
flags, but I want to first get the ability to pass these flags plumbed
into the VFS layer and the code points for O_HOT and O_COLD reserved.

Ted, you still remember the directory-block read-ahead patches I sent 
last year for ext4 and which you declined, as it would add another mount 
parameter for ext4?

http://www.digipedia.pl/usenet/thread/11916/24502/#post24502


If an application could use those flags to the file system (and then not 
only ext4, but any file system) to indicate a certain directory is 
important and frequently accessed, it would be simple to update those 
patches to work without another mount option.
And while I updating our FhGFS meta data on disk layout to workaround 
the general problem we, we (and for example Lustre) are still affected 
the object-storage-side.


Thanks,
Bernd