On Tue, Jun 19 2012 at 9:25am -0400, Lukáš Czerner <lczerner@xxxxxxxxxx> wrote: > On Tue, 19 Jun 2012, Mike Snitzer wrote: > > > Date: Tue, 19 Jun 2012 09:16:49 -0400 > > From: Mike Snitzer <snitzer@xxxxxxxxxx> > > To: Lukáš Czerner <lczerner@xxxxxxxxxx> > > Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Spelic <spelic@xxxxxxxxxxxxx>, > > device-mapper development <dm-devel@xxxxxxxxxx>, > > linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx > > Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard > > > > On Tue, Jun 19 2012 at 2:32am -0400, > > Lukáš Czerner <lczerner@xxxxxxxxxx> wrote: > > > > > So do I understand correctly that even though the discard came > > > through and thinp took advantage of it it still returns EOPNOTSUPP ? > > > > No, not correct. Why are you assuming this? I must be missing > > something from this discussion that led you there. > > Those two paragraphs led me to that conclusion: > > That message says the underlying device doesn't support discards > (because it is an MD device). But the thinp device still has discards > enabled -- it just won't pass the discards down to the underlying data > device. > > The discards still inform the thin-pool that the corresponding extents > are no longer allocated. > > so I am a bit confused now. Why the dm-thin returned EOPNOTSUPP then > ? Is that because it has been configured to ignore_discard, or it > actually takes advantage of the discard but underlying device does > not support it (and no_discard_passdown is not set) so it return > EOPNOTSUPP ? > > > > > > This seems rather suboptimal. IIRC there was a discussion to add an > > > option to enable/disable sending discard in thinp target down > > > to the device. > > > > > > So maybe it might be a bit smarter than that and actually > > > enable/disable discard pass through depending on the underlying > > > support, so we do not blindly send discard down to the device even > > > though it does not support it. > > > > Yes, that is what we did. > > > > Discards are enabled my default (including discard passdown), but if the > > underlying data device doesn't support discards then the discards will > > not be passed down. > > > > And here are the feature controls that can be provided when loading the > > thin-pool's DM table: > > > > ignore_discard: disable discard > > no_discard_passdown: don't pass discards down to the data device > > > > -EOPNOTSUPP is only ever returned if 'ignore_discard' is provided. > > Ok, so in this case 'ignore_discard' has been configured ? I don't recall Spelic saying anything about EOPNOTSUPP. So what has made you zero in on an -EOPNOTSUPP return (which should not be happening)? -- 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
