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Re: [Qemu-block] [PATCH 3/4] qcow2: Discard preallocated zero clusters
From: |
Eric Blake |
Subject: |
Re: [Qemu-block] [PATCH 3/4] qcow2: Discard preallocated zero clusters |
Date: |
Wed, 3 May 2017 19:58:54 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0 |
On 05/03/2017 06:11 PM, Max Reitz wrote:
> In discard_single_l2(), we completely discard normal clusters instead of
> simply turning them into preallocated zero clusters. That means we
> should probably do the same with such preallocated zero clusters:
> Discard them instead of keeping them allocated.
>
> Reported-by: Eric Blake <address@hidden>
> Signed-off-by: Max Reitz <address@hidden>
> ---
> block/qcow2-cluster.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
Reviewed-by: Eric Blake <address@hidden>
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index fb91fd8979..31077d8102 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1511,7 +1511,8 @@ static int discard_single_l2(BlockDriverState *bs,
> uint64_t offset,
> break;
>
> case QCOW2_CLUSTER_ZERO:
> - if (!full_discard) {
> + /* Preallocated zero clusters should be discarded in any
> case */
> + if (!full_discard && (old_l2_entry & L2E_OFFSET_MASK) == 0) {
Again, if we had a separate QCOW2_CLUSTER_* for plain vs. pre-allocated
zero, this might be easier to write.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-block] [PATCH 0/4] qcow2: Some fixes, Max Reitz, 2017/05/03
- [Qemu-block] [PATCH 1/4] qcow2: Fix preallocation size formula, Max Reitz, 2017/05/03
- [Qemu-block] [PATCH 2/4] qcow2: Reuse preallocated zero clusters, Max Reitz, 2017/05/03
- [Qemu-block] [PATCH 3/4] qcow2: Discard preallocated zero clusters, Max Reitz, 2017/05/03
- Re: [Qemu-block] [PATCH 3/4] qcow2: Discard preallocated zero clusters,
Eric Blake <=
- [Qemu-block] [PATCH 4/4] iotests: Extend test 066, Max Reitz, 2017/05/03
- Re: [Qemu-block] [PATCH 0/4] qcow2: Some fixes, Kevin Wolf, 2017/05/04