[xfs-masters] how to use fstrim?

[Dave Chinner]

On Tue, Jul 30, 2013 at 09:37:15PM +0200, Stefan Priebe wrote:
> Am 27.07.2013 03:50, schrieb Dave Chinner:
> >On Fri, Jul 26, 2013 at 08:17:21PM +0200, Stefan Priebe wrote:
> >>Hi,
> >>
> >>what is the right way to use fstrim on top of XFS? just doing fstrim
> >>-v -m 4194304 /
> >>
> >>results sometimes (might depend on disk i/o) to hanging tasks and
> >>stack traces - fstrim needs > 5 min in these cases.
> >
> >It does indeed depend on disk IO. XFS walks all the free space and
> >issues discards on it, so runtime is always O(freespace). And while
> >it is walking an AG discarding the free space, it will hold the AG
> >locked so that free space doesn't change. This can hang other
> >operations for the length of time it takes to discard all the free
> >space in the AG.
> > IOWs, the behaviour of fstrim on XFS is entirely dependent on the
> > speed of the block layer and hardware implementations of discards.
> 
> Yes OK i understand that but is there any way to prevent getting the
> whole server crash when I/O is too much?

Sorry, what crash are you talking about? IO being slow because you
ran fstrim isn't a crash....

> For example splitting whole disk or even AGs into subparts? Or set a
> timeout for the fstrim command?

You can split fstrim up into smaller sections yourself by using the
range parameters.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com