linux-ext4 - Re: fstrim has no effect on a just-mounted filesystem

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Date:	Wed, 12 Mar 2014 18:24:16 +0000
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: fstrim has no effect on a just-mounted filesystem

On Wed, Mar 12, 2014 at 07:10:42PM +0100, Paolo Bonzini wrote:
> Il 12/03/2014 11:17, Richard W.M. Jones ha scritto:
> >Somewhere, the discard requests are disappearing in the stack (or more
> >likely, being delayed).  blktrace/trace-cmd somehow forces them out.
> >But fsync/sync/umount/sleep does not.  They might be stuck in qemu too ...
> 
> No, this I can be quite sure about.  QEMU sends them as soon as they
> are received in the SCSI layer.  If they were ill-formed, QEMU would
> fail them.  If they got stuck, sooner or later you'd not be able to
> do I/O anymore (there is a queue depth limit) and the guest would
> start getting timeouts.
> 
> Also, certainly blktrace would have no effect on QEMU.

Yup, it was completely a bug at my end.  Now that is fixed,
fstrim works perfectly.

Rich.

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Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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