linux-kernel - Re: [PATCH 2/2] [RESEND] add discard support to nbd

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Date:	Fri, 31 Aug 2012 11:24:31 -0400
From:	Paul Clements <paul.clements@...sios.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] [RESEND] add discard support to nbd

On Thu, Aug 30, 2012 at 6:03 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 29 Aug 2012 08:41:02 -0400
> paul.clements@...eleye.com wrote:
>
>> Description: This patch adds discard support to nbd. When the nbd client
>> system receives a discard request, this will be passed along to the nbd
>> server system, where the nbd-server will respond by performing:
>>       fallocate(.. FALLOC_FL_PUNCH_HOLE ..)
>>
>> To punch a hole in the backend storage, which is no longer needed.
>>
>
> What happens if the user is running an older server?

In that case, the older server will not have set NBD_SEND_FLAG_TRIM,
so QUEUE_FLAG_DISCARD doesn't get set, so no discards will be sent to
the device.

> I is it possible that because the old server didn't set
> NBD_FLAG_SEND_TRIM, the user's screen gets filled with WARN_ONs?

No.

> Anyway, please make sure this combination was tested!

It was.

Thanks for the feedback.

I will resend v2 of the patches shortly.

--
Paul
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