Hi Greg,
Thanks for your answer. I did
$ mount -t ext4 -o discard /dev/rbd1 /mnt
# did not see any DISCARD op after that
$ fstrim /mnt
# neither
Maybe missing something there ? I expected '-o discard' to be enough ?
On 01/30/14 16:24, Gregory Farnum wrote:
On Thu, Jan 30, 2014 at 1:31 AM, Jean-Tiare LE BIGOT
<jean-tiare.le-bigot@xxxxxxx> wrote:
Hi,
I started to implement 'DISCARD' support in RBD kernel driver as described
on http://tracker.ceph.com/issues/190
This first (easy) step was to add at the end of
drivers/block/rbd.c:rbd_init_disk
/* Advertise discard support for aligned blocks */
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
disk->queue->limits.discard_granularity = segment_size;
disk->queue->limits.discard_alignment = segment_size;
With this both 'mount -o discard' and 'fstrim' stopped to complain about
missing 'DISCARD' support. Good !
Next step was to add support on `rbd_request_fn` which I did (sort of). But
here I'm stuck. If I understood well FS drivers uses `REQ_DISCARD` flag of
`rq->cmd_flags` to notify the driver of the discard operation. But the
problem is that (rq->cmd_flags & REQ_DISCARD) never appears to be set.
I tried copying then removing large files, lots of small files, forcing
fstrim. But I never got it. I must be missing something obvious but I can't
manage to find what ? Do you have any clue what could be wrong ?
I don't know anything about the relevant kernel internal interfaces
here, but don't most FSes need to be told explicitly to do trimming?
Did you do that?
-Greg
Software Engineer #42 @ http://inktank.com | http://ceph.com
--
Jean-Tiare, shared-hosting team
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