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Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for e
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster |
Date: |
Fri, 14 Apr 2017 14:00:15 +0800 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Thu, 04/13 10:34, address@hidden wrote:
> From: Lidong Chen <address@hidden>
>
> BLOCK_SIZE is (1 << 20), qcow2 cluster size is 65536 by default,
> this may cause the qcow2 file size to be bigger after migration.
> This patch checks each cluster, using blk_pwrite_zeroes for each
> zero cluster.
>
> Reviewed-by: Stefan Hajnoczi <address@hidden>
> Signed-off-by: Lidong Chen <address@hidden>
> ---
> v6 changelog:
> Fix up some grammar in the comment.
> ---
> migration/block.c | 35 +++++++++++++++++++++++++++++++++--
> 1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/migration/block.c b/migration/block.c
> index 7734ff7..41c7a55 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -885,6 +885,8 @@ static int block_load(QEMUFile *f, void *opaque, int
> version_id)
> int64_t total_sectors = 0;
> int nr_sectors;
> int ret;
> + BlockDriverInfo bdi;
> + int cluster_size;
>
> do {
> addr = qemu_get_be64(f);
> @@ -919,6 +921,15 @@ static int block_load(QEMUFile *f, void *opaque, int
> version_id)
> error_report_err(local_err);
> return -EINVAL;
> }
> +
> + ret = bdrv_get_info(blk_bs(blk), &bdi);
> + if (ret == 0 && bdi.cluster_size > 0 &&
> + bdi.cluster_size <= BLOCK_SIZE &&
> + BLOCK_SIZE % bdi.cluster_size == 0) {
> + cluster_size = bdi.cluster_size;
> + } else {
> + cluster_size = BLOCK_SIZE;
> + }
> }
>
> if (total_sectors - addr < BDRV_SECTORS_PER_DIRTY_CHUNK) {
> @@ -932,10 +943,30 @@ static int block_load(QEMUFile *f, void *opaque, int
> version_id)
> nr_sectors * BDRV_SECTOR_SIZE,
> BDRV_REQ_MAY_UNMAP);
> } else {
> + int i;
> + int64_t cur_addr;
> + uint8_t *cur_buf;
> +
> buf = g_malloc(BLOCK_SIZE);
> qemu_get_buffer(f, buf, BLOCK_SIZE);
> - ret = blk_pwrite(blk, addr * BDRV_SECTOR_SIZE, buf,
> - nr_sectors * BDRV_SECTOR_SIZE, 0);
> + for (i = 0; i < BLOCK_SIZE / cluster_size; i++) {
> + cur_addr = addr * BDRV_SECTOR_SIZE + i * cluster_size;
> + cur_buf = buf + i * cluster_size;
> +
> + if ((!block_mig_state.zero_blocks ||
> + cluster_size < BLOCK_SIZE) &&
> + buffer_is_zero(cur_buf, cluster_size)) {
> + ret = blk_pwrite_zeroes(blk, cur_addr,
> + cluster_size,
> + BDRV_REQ_MAY_UNMAP);
> + } else {
> + ret = blk_pwrite(blk, cur_addr, cur_buf,
> + cluster_size, 0);
> + }
> + if (ret < 0) {
> + break;
> + }
> + }
> g_free(buf);
> }
Sorry for asking this question so late, but, before it gets too late: did you
evaluate the performance impact of this change under real world workload?
Effectively, if no cluster is zero, this patch still splits a big write into
small ones, which is the opposition of usual performance optimizations (i.e.
trying to coalesce requests).
Fam
- [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, jemmy858585, 2017/04/12
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, Stefan Hajnoczi, 2017/04/13
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster,
Fam Zheng <=
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/14
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, Fam Zheng, 2017/04/16
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/17
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, Fam Zheng, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, Fam Zheng, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, 858585 jemmy, 2017/04/24
- Re: [Qemu-devel] [PATCH v6] migration/block: use blk_pwrite_zeroes for each zero cluster, Fam Zheng, 2017/04/24