linux-ext4 - Re: Fwd: block level cow operation

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Message-ID: <CAD6i1fKzoWdqaBRzTh1xMu9thc=9GCGbvz3eyi3yzeTMNgBApg@mail.gmail.com>
Date:	Thu, 25 Apr 2013 18:30:18 +0530
From:	Prashant Shah <pshah.mumbai@...il.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Fwd: block level cow operation

Hi,

On Tue, Apr 9, 2013 at 8:16 PM, Dmitry Monakhov <dmonakhov@...nvz.org> wrote:
>
> you should not block bio/requests handling, but simply deffer original
> bio. Some things like that:
>
> OUR_MAIN_ENTERING_POINT {
>   if (bio->bi_rw == WRITE) {
>      if (cow_required(bio))
>        cow_bio  = create_cow_copy(bio)
>        submit_bio(cow_bio);
>    }
>   /* Cow is not required */
>    submit_bio(bio);
> }

> This approach gives us reasonable performance ~3 times slower than disk
> throughput.
> For a reference implementation you may look at driver/dm/dm-snap or to
> Acronis snapapi module (AFAIR it is opensource)
> }

Thanks. That is what I was looking for. Got the ref code from snapapi
module which is opensource.

Its not something that is specific to any filesystem.

Regards.
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