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Re: [Qemu-devel] [Qemu-block] [PATCH v2] qcow2: do not allocate extra me
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH v2] qcow2: do not allocate extra memory |
Date: |
Thu, 14 Jul 2016 15:04:20 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 07/14/2016 12:59 PM, Vladimir Sementsov-Ogievskiy wrote:
> There are no needs to allocate more than one cluster, as we set
> avail_out for deflate to one cluster.
>
> Zlib docs (http://www.zlib.net/manual.html) says:
> "deflate compresses as much data as possible, and stops when the input
> buffer becomes empty or the output buffer becomes full."
>
> So, deflate will not write more than avail_out to output buffer. If
> there is no enough space in output buffer for compressed data (it may be
> larger than input data) deflate just returns Z_OK. (if all data is
> compressed and written to output buffer deflate returns Z_STREAM_END).
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
>
> v2: improve commit message
>
> block/qcow.c | 2 +-
> block/qcow2.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block/qcow.c b/block/qcow.c
> index ac849bd..d8826f3 100644
> --- a/block/qcow.c
> +++ b/block/qcow.c
> @@ -983,7 +983,7 @@ static int qcow_write_compressed(BlockDriverState *bs,
> int64_t sector_num,
> return ret;
> }
>
> - out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
> + out_buf = g_malloc(s->cluster_size);
>
> /* best compression, small window, no zlib header */
> memset(&strm, 0, sizeof(strm));
> diff --git a/block/qcow2.c b/block/qcow2.c
> index a5ea19b..b1c90ae 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2612,7 +2612,7 @@ static int qcow2_write_compressed(BlockDriverState *bs,
> int64_t sector_num,
> return ret;
> }
>
> - out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
> + out_buf = g_malloc(s->cluster_size);
>
> /* best compression, small window, no zlib header */
> memset(&strm, 0, sizeof(strm));
>
Reviewed-by: John Snow <address@hidden>