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[Qemu-block] [PATCH v2 06/12] block/io: bdrv_co_do_copy_on_readv: lazy a
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
[Qemu-block] [PATCH v2 06/12] block/io: bdrv_co_do_copy_on_readv: lazy allocation |
Date: |
Tue, 4 Jun 2019 19:15:08 +0300 |
Allocate bounce_buffer only if it is really needed. Also, sub-optimize
allocation size (why not?).
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
block/io.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/block/io.c b/block/io.c
index efd2b80293..a4f67aca47 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1171,7 +1171,7 @@ 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;
@@ -1206,14 +1206,6 @@ 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;
@@ -1240,6 +1232,17 @@ 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,
--
2.18.0
- [Qemu-block] [PATCH v2 00/12] block: qiov_offset parameter for io, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 12/12] block/qcow2: implement .bdrv_co_pwritev(_compressed)_part, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 10/12] block/qcow2: refactor qcow2_co_preadv to use buffer-based io, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 08/12] block/io: bdrv_aligned_pwritev: use and support qiov_offset, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 07/12] block/io: bdrv_aligned_preadv: use and support qiov_offset, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 06/12] block/io: bdrv_co_do_copy_on_readv: lazy allocation,
Vladimir Sementsov-Ogievskiy <=
- [Qemu-block] [PATCH v2 01/12] util/iov: introduce qemu_iovec_init_extended, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 02/12] util/iov: improve qemu_iovec_is_zero, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 05/12] block/io: bdrv_co_do_copy_on_readv: use and support qiov_offset, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 11/12] block/qcow2: implement .bdrv_co_preadv_part, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 04/12] block: define .*_part io handlers in BlockDriver, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 03/12] block/io: refactor padding, Vladimir Sementsov-Ogievskiy, 2019/06/04
- [Qemu-block] [PATCH v2 09/12] block/io: introduce bdrv_co_p{read, write}v_part, Vladimir Sementsov-Ogievskiy, 2019/06/04
- Re: [Qemu-block] [Qemu-devel] [PATCH v2 00/12] block: qiov_offset parameter for io, no-reply, 2019/06/05
- Re: [Qemu-block] [Qemu-devel] [PATCH v2 00/12] block: qiov_offset parameter for io, Stefan Hajnoczi, 2019/06/28