Re: [Qemu-devel] [PATCH v2] qcow2: discard bitmap when removed

[Max Reitz <mreitz@redhat.com>]

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On 28.02.19 10:26, Andrey Shinkevich wrote:
> When a bitmap is removed, we can clean some space on the disk. The size
> of a cluster may be larger, so is the size of the bitmap that includes
> many clusters. Some bitmaps can be as large as tens of megabytes.
> The flag QCOW2_DISCARD_ALWAYS allows a call to the raw_co_pdiscard()
> that does the actual cleaning of the image on disk, while with the flag
> QCOW2_DISCARD_OTHER, a reference count of the cluster is updated only.
> 
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
> v1: Discard old bitmap directories in QCOW2 image
> 
> In the first version of the patch, any call to qcow2_free_clusters() in
> block/qcow2-bitmap.c was with the flag QCOW2_DISCARD_ALWAYS, even in the
> cases when the cleaned space is insignificant, particularly, in case of
> bitmap directories.
> Discussed in the email thread with the message ID
> <1549974951-731285-1-git-send-email-andrey.shinkevich@virtuozzo.com>
> 
>  block/qcow2-bitmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, changed the commit message to Vladimir’s proposal and applied to
my block-next branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block-next

Max


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