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Re: [Qemu-block] [PATCH V3] block/iscsi: allow caching of the allocation

From: Fam Zheng
Subject: Re: [Qemu-block] [PATCH V3] block/iscsi: allow caching of the allocation map
Date: Sun, 12 Jun 2016 13:04:42 +0800
User-agent: Mutt/1.6.1 (2016-04-27)

On Tue, 05/24 10:40, Peter Lieven wrote:
> until now the allocation map was used only as a hint if a cluster
> is allocated or not. If a block was not allocated (or Qemu had
> no info about the allocation status) a get_block_status call was
> issued to check the allocation status and possibly avoid
> a subsequent read of unallocated sectors. If a block known to be
> allocated the get_block_status call was omitted. In the other case
> a get_block_status call was issued before every read to avoid
> the necessity for a consistent allocation map. To avoid the
> potential overhead of calling get_block_status for each and
> every read request this took only place for the bigger requests.
> This patch enhances this mechanism to cache the allocation
> status and avoid calling get_block_status for blocks where
> the allocation status has been queried before. This allows
> for bypassing the read request even for smaller requests and
> additionally omits calling get_block_status for known to be
> unallocated blocks.
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> v2->v3: - fix wording errors [Fam]
>         - reinit allocmap only if allocmap is present in
>           bdrv_reopen_commit

I did an incremental review and the diff-of-diff looks good to me, so:

Reviewed-by: Fam Zheng <address@hidden>

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