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

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Message-ID: <5320A322.7020009@redhat.com>
Date:	Wed, 12 Mar 2014 19:10:42 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Richard W.M. Jones" <rjones@...hat.com>,
	Eric Sandeen <sandeen@...hat.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: fstrim has no effect on a just-mounted filesystem

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.

Paolo
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