Seems to me a trim should have higher priority than scrub. One rationale for this is that a trim can free up underlying storage, allowing the device to take some actions that can actually make subsequent I/Os (write I/Os at any rate) go faster. If the scrub is going to cause any write activity, this would be a net win. :-)
The counter argument for this is that the trim is usually just an "optimization" or "garbage collection" activity, which can be run in the background, whereas the scrub might represent a user-initiated action, and it does make sense to prioritize explicit user actions. On Sat, Nov 30, 2013 at 8:33 AM, Andriy Gapon <[email protected]> wrote: > on 30/11/2013 17:55 George Wilson said the following: > > Andriy, > > > > The fix looks good but I have a couple of questions: > > > > 1. Are you sure you want the TRIM priority to be lower than SCRUB? > > I am not sure but I think that that's how we had it prior to 4045: > > http://bxr.su/FreeBSD/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zio.c#69 > > > 2. You have zfs_vdev_trim_max_active set to 1 with an /* XXX */ next to > it. Does > > this mean you haven't settled on the final value for active max? > > That was the gist of my question - what zfs_vdev_trim_max_active and > zfs_vdev_trim_min_active should be. Hence the "XXX". > > > On 11/30/13 10:13 AM, Andriy Gapon wrote: > >> [resending with CC fixed] > >> > >> Matt, > >> > >> as you most likely know, ZFS/FreeBSD already has ability to use TRIM > command > >> with disks that support it. > >> As the command can be quite slow and it is a maintenance kind of > command, it > >> makes sense to assign a very low priority to it. > >> > >> I've come up with the following change that introduces a new priority > for the > >> TRIM zios: > >> http://people.freebsd.org/~avg/zfs-trim-priority.diff > >> To be honest, this change actually attempts to restore what we already > had in > >> FreeBSD before I merged your write throttle & i/o scheduler performance > work. > >> > >> Could you please review the change? > >> I am not sure if I correctly translated my intent to the min_active and > >> max_active values. I will greatly appreciate your help with these. > >> > >> Thank you! > >> > >> > >> _______________________________________________ > >> developer mailing list > >> [email protected] > >> http://lists.open-zfs.org/mailman/listinfo/developer > > > > > -- > Andriy Gapon > _______________________________________________ > developer mailing list > [email protected] > http://lists.open-zfs.org/mailman/listinfo/developer >
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