On 07/30/2012 07:57 AM, Paolo Bonzini wrote:
> Il 30/07/2012 15:51, Richard W.M. Jones ha scritto:
>>>> Or just finish up discard support and use the existing fstrim command of
>>>> qemu-ga. :)
>> What's actually involved to do this? I noticed that a virtio-scsi on
>> qcow2 v3 device exported to the guest does not appear to support TRIM
>> at all (see attached test script and output).
>
> The most basic thing to do is to pass -device discard_granularity=NNN,
> where NNN should be the cluster size of the device. On top of this you
> need to add the ability to do TRIM asynchronously, quite some testing,
> and perhaps improving the disk formats so that they support
> sector-granularity discard.
>
> Patches for asynchronous TRIM are in the works (the threadpool patches
> on the list are the first step).
>
> Long term I would like the ability to distinguish
> discard-for-thin-provisioning ("may cause fragmentation, all subsequent
> accesses could be slower") from discard-for-wear-leveling ("only the
> first subsequent access would be slowed down"). This requires changes
> at all levels (host kernel, QEMU, management, guest kernel, and possibly
> guest applications).Ooh, nice bullet point to add to my upcoming presentation at Linux Plumber's Conference in a month: http://summit.linuxplumbersconf.org/lpc-2012/meeting/33/lpc2012-ref-improved-virt-disk-handling/ Does anyone else have some annoyances about large sparse file handling where improving the kernel would make our life easier, that I should incorporate into my discussion? -- Eric Blake [email protected] +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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