Andrew Morton wrote:
On Tue, 14 Jul 2009 17:05:54 +0300
Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
Speed up ext3 recovery mount time by not sync'ing the
block device. Instead place all dirty buffers into the
I/O queue and add a write barrier. This ensures that
no subsequent write will reach the disk before all the
recovery writes, but that we do not have to wait for the
I/O.
Note that ext3 reads sectors the correct way: through the
buffer cache, so there is no risk of reading old metadata.
hm. The change seems reasonable to me. afaict it leaves no timing
windows during which another crash could muck things up.
As long as those write barriers actually work. Do they? For all
conceivable devices and IO schedulers?
As far as I know I/O barriers work. The I/O schedulers are forcibly
drained so they do not affect the barrier. I am not sure about all
devices - I guess some device drivers might return errors if asked to
provide a barrier and they can't.
Our device is a MMC and does one I/O at a time, so hardware barriers
are not needed and are ignored.
It would be useful if you could quantify the benefits please - some
before-and-after timing results with both your funky hardware as well
as regular old disks would suit.
I will send some examples.
I'd suggest that if we're going to do this, we should aim to do it
unconditionally - no mount option needed. We could leave the option
there for a while, for testing purposes (ie: we think the code might be
buggy). But the new feature should perhaps default to "on", and we
plan to remove the mount option after a while.
Because there's no reason to retain the mount option in the long term.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
