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RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup
From: |
Shahar Frank |
Subject: |
RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup |
Date: |
Wed, 3 Sep 2008 00:35:19 -0700 |
> -----Original Message-----
> From: Laurent Vivier [mailto:address@hidden
> Sent: Wednesday, September 03, 2008 10:10 AM
> To: address@hidden
> Cc: Shahar Frank
> Subject: Re: [Qemu-devel][PATCH,RFC] Zero cluster dedup
>
>
> Is it really needed to have a shared zero page ?
>
> When I read qcow_read() and qcow_aio_read_cb() I see:
>
> if (!cluster_offset) {
> ...
> memset(buf, 0, 512 * n);
> ...
> }
> and so I think you have just to clear the l2_table entry for the given
> clusters (and free them).
You are correct if this is a standalone image i.e. without backing file. If the
image has a backing file, a zero mapping is interpreted as "read it from the
backing file at the same (logical) offset".
I could add some other special value for it but I wanted to preserve backwards
compatibility, and it also looks "dirty" to have several special values for
such features.
>
> Regards,
> Laurent
> --
> ----------------- address@hidden ------------------
> "La perfection est atteinte non quand il ne reste rien à
> ajouter mais quand il ne reste rien à enlever." Saint Exupéry
Shahar
Re: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Kevin Wolf, 2008/09/03
- RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Shahar Frank, 2008/09/03
- Re: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Kevin Wolf, 2008/09/03
- RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Shahar Frank, 2008/09/03
- RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Laurent Vivier, 2008/09/03
- RE: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Shahar Frank, 2008/09/03
Re: [Qemu-devel][PATCH,RFC] Zero cluster dedup, Laurent Vivier, 2008/09/03