Re: Agressive selective pre-allocation

["Ragnar Kjørstad" <reiserfs@ragnark.vestdata.no>]

On Tue, Dec 10, 2002 at 05:13:13PM +0300, Hans Reiser wrote:
> >An alternative would be the possibility to tell the fs about the
> >properties of the files. Maybe an ioctl to notify the fs that for this
> >particular file the fs should allocate X blocks at the time? That would
> >ensure that the files only get limited fragmentation and performance
> >stays optimal.
>
> Veritas did this, and then their architect regretted that nobody 
> actually used that code and advised me not to do it.  You may have an 
> advantage with open source though in that you can modify the important 
> user space programs to use it.

I was more thinking along the lines of:
find /var/log -type f | xargs ioctl REISERFS_SLOW_GROWING

But I guess syslog or whatever is used would have to be modified
for it to happen automaticly on new files. My guess is that
syslog-maintainers would not take patches for features like this unless
it was done in a more generic way that could potentially be used by
other filesystems as well. 


> We have some block preallocation code in V3 for files that are kept open 
> while being written to.  You can look at that code if you want.  You can 
> also write a plugin for v4 that does what you want.

Are you talking about the allocate on flush code? I'll check that out;
allthough at this point it is of course more interesting to write code
for reiserfs4 than v3 - in particular if the new improved infrastructure
makes it easier.

> While I will not take someone off another task to work on this, I will 
> be open to patches from others.

As I wrote in my original mail I don't have time to really work on this
now, but maybe later.



-- 
Ragnar Kjørstad