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block/io: bdrv_co_do_copy_on_readv: lazy allocation

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Allocate bounce_buffer only if it is really needed. Also, sub-optimize
allocation size (why not?).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190604161514.262241-7-vsementsov@virtuozzo.com
Message-Id: <20190604161514.262241-7-vsementsov@virtuozzo.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2019-06-04 19:15:08 +03:00 committed by Stefan Hajnoczi
parent 1143ec5ebf
commit 2275cc90a1
1 changed files with 12 additions and 9 deletions
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21
block/io.c
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@ -1236,7 +1236,7 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
* modifying the image file. This is critical for zero-copy guest I/O
* where anything might happen inside guest memory.
*/
void *bounce_buffer;
void *bounce_buffer = NULL;
BlockDriver *drv = bs->drv;
int64_t cluster_offset;
@ -1271,14 +1271,6 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
trace_bdrv_co_do_copy_on_readv(bs, offset, bytes,
cluster_offset, cluster_bytes);
bounce_buffer = qemu_try_blockalign(bs,
MIN(MIN(max_transfer, cluster_bytes),
MAX_BOUNCE_BUFFER));
if (bounce_buffer == NULL) {
ret = -ENOMEM;
goto err;
}
while (cluster_bytes) {
int64_t pnum;
@ -1305,6 +1297,17 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
/* Must copy-on-read; use the bounce buffer */
pnum = MIN(pnum, MAX_BOUNCE_BUFFER);
if (!bounce_buffer) {
int64_t max_we_need = MAX(pnum, cluster_bytes - pnum);
int64_t max_allowed = MIN(max_transfer, MAX_BOUNCE_BUFFER);
int64_t bounce_buffer_len = MIN(max_we_need, max_allowed);
bounce_buffer = qemu_try_blockalign(bs, bounce_buffer_len);
if (!bounce_buffer) {
ret = -ENOMEM;
goto err;
}
}
qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
ret = bdrv_driver_preadv(bs, cluster_offset, pnum,