On 09/29/2010 08:59 PM, Lennart Poettering wrote:
On Wed, 29.09.10 16:25, Ric Wheeler (rwhee...@redhat.com) wrote:
This in fact is how all current readahead implementations work, be it
the fedora, the suse or ubuntu's readahead or Arjan's sreadahead. What's
new is that in the systemd case we try to test for ssd/rotating
properly, instead of just hardcoding a check for
/sys/class/block/sda/queue/rotational.
A couple of questions pop into mind - is systemd the right place to
automatically tune readahead? If this is a generic feature for the
type of device, it sounds like something that we should be doing
somewhere else in the stack (not relying on tuning from user space).
Note that this is not the kind of readahead that is controllable via
/sys/class/block/sda/queue/read_ahead_kb, this is about detecting "hot"
files at boot, and then preloading them on the next boot. i.e. the
problem Jens once proposed fcache for.
Second question is why is checking in /sys a big deal, would you
prefer an interface like we did for alignment in libblkid?
Well, currently there's no way to discover the underlying block devices
if you have a btrfs mount point. This is what Josef's patch added for
us.
Lennart
Makes sense to me,thanks!
Ric
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