Re: [PATCH v2 1/5] add metadata_incore ioctl in vfs

On Wednesday 05 January 2011 03:17:16 Shaohua Li wrote:

On Tue, 2011-01-04 at 17:40 +0800, Arnd Bergmann wrote:

quoted

Have you tried passing just a single metadata_incore_ent
at the ioctl and looping in user space? I would guess the
extra overhead of that would be small enough, but that might
need to be measured.

metadata usually isn't continuous, so this means we have a lot of
metadata_incore_ent entries. And this is called at boot time and I want
to make the overhead as low as possible to not impact boot. Unless there
are certain reasons we can't use indirect pointers, I'd like to make
kernel return a vector of entries.

It's not a strict rule, but the indirect data passing is rather
ugly and I'd only do that if the difference can be /measured/.

If the purpose is to speed up boot time by preloading metadata,
the FIMETADATA_INCORE operations should of course not take a
significant amount of time compared to the actual preloading,
but as long as it's less than one percent of the time you need
for the preload, I would just use the simpler interface.

This change can go away as well.

Two more general comments:

- You probably want to add the ioctls to file_ioctl instead of do_vfs_ioctl,
  so you don't add another case statement to the common path.

- I don't know if there are any rules for what should be an ioctl or an
  fcntl, we're rather inconsistent about this. If you have found a good
  reason for making it an ioctl, just put that into the changelog so we
  can refer to it next time.

	Arnd