[linux-lvm] [PATCH] dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM wi

[DarkNovaNick at gmail.com]

On Apr 13, 2011 5:40pm, Mike Snitzer <snitzer at redhat.com> wrote:

> Unfortunately, the failed discard to the snapshot-origin device disables

> ext4's discards for the entire volume (even after you remove the

> snapshot).



> But the following patch fixes that:



> Subject: dm snapshot: add discard support to the snapshot-origin target



> Allow the snapshot-origin target to pass discards to the origin device

> (after any copyout of the region being discarded; but generally speaking

> that copyout won't be needed as the region will have already been copied

> to the cow).



> So for example, when you remove a file from an ext4 mounted origin

> volume it triggers copyout to the snapshot. When the DISCARD is then

> issued during the subsequent journal commit no copyout is needed.



> Signed-off-by: Mike Snitzer snitzer at redhat.com>

> ---

> drivers/md/dm-snap.c | 3 ++-

> 1 files changed, 2 insertions(+), 1 deletions(-)



> diff --git a/drivers/md/dm-snap.cb/drivers/md/dm-snap.c

> index a2d3309..028d216 100644

> --- a/drivers/md/dm-snap.c

> +++ b/drivers/md/dm-snap.c

> @@ -2076,6 +2076,7 @@ static int origin_ctr(struct dm_target *ti,  
> unsigned int argc, char **argv)



> ti->private = dev;

> ti->num_flush_requests = 1;

> + ti->num_discard_requests = 1;



> return 0;

> }

> @@ -2153,7 +2154,7 @@ static int origin_iterate_devices(struct dm_target  
> *ti,



> static struct target_type origin_target = {

> .name = "snapshot-origin",

> - .version = {1, 7, 1},

> + .version = {1, 8, 0},

> .module = THIS_MODULE,

> .ctr = origin_ctr,

> .dtr = origin_dtr,



Thanks, I will put that patch in my kernel. Do you anticipate this change  
making its way into the main kernel source at some point in the future?  
Thanks again,

Nick
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