backup_cow_with_offload can transfer more than one cluster. Let
backup_cow_with_bounce_buffer behave similarly. It reduces the number
of IO requests, since there is no need to copy cluster by cluster.
Logic around bounce_buffer allocation changed: we can't just allocate
one-cluster-sized buffer to share for all iterations. We can't also
allocate buffer of full-request length it may be too large, so
BACKUP_MAX_BOUNCE_BUFFER is introduced. And finally, allocation logic
is to allocate a buffer sufficient to handle all remaining iterations
at the point where we need the buffer for the first time.
Bonus: get rid of pointer-to-pointer.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
block/backup.c | 65 +++++++++++++++++++++++++++++++-------------------
1 file changed, 41 insertions(+), 24 deletions(-)
diff --git a/block/backup.c b/block/backup.c
index d482d93458..65f7212c85 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -27,6 +27,7 @@
#include "qemu/error-report.h"
#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
+#define BACKUP_MAX_BOUNCE_BUFFER (64 * 1024 * 1024)
typedef struct CowRequest {
int64_t start_byte;
@@ -98,44 +99,55 @@ static void cow_request_end(CowRequest *req)
qemu_co_queue_restart_all(&req->wait_queue);
}
-/* Copy range to target with a bounce buffer and return the bytes copied. If
- * error occurred, return a negative error number */
+/*
+ * Copy range to target with a bounce buffer and return the bytes copied. If
+ * error occurred, return a negative error number
+ *
+ * @bounce_buffer is assumed to enough to store
+ * MIN(BACKUP_MAX_BOUNCE_BUFFER, @end - @start) bytes
+ */
static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
int64_t start,
int64_t end,
bool is_write_notifier,
bool *error_is_read,
- void **bounce_buffer)
+ void *bounce_buffer)
{
int ret;
BlockBackend *blk = job->common.blk;
- int nbytes;
+ int nbytes, remaining_bytes;
int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
assert(QEMU_IS_ALIGNED(start, job->cluster_size));
- bdrv_reset_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
- nbytes = MIN(job->cluster_size, job->len - start);
- if (!*bounce_buffer) {
- *bounce_buffer = blk_blockalign(blk, job->cluster_size);
- }
+ bdrv_reset_dirty_bitmap(job->copy_bitmap, start, end - start);
+ nbytes = MIN(end - start, job->len - start);
- ret = blk_co_pread(blk, start, nbytes, *bounce_buffer, read_flags);
- if (ret < 0) {
- trace_backup_do_cow_read_fail(job, start, ret);
- if (error_is_read) {
- *error_is_read = true;
+
+ remaining_bytes = nbytes;
+ while (remaining_bytes) {
+ int chunk = MIN(BACKUP_MAX_BOUNCE_BUFFER, remaining_bytes);
+
+ ret = blk_co_pread(blk, start, chunk, bounce_buffer, read_flags);
+ if (ret < 0) {
+ trace_backup_do_cow_read_fail(job, start, ret);
+ if (error_is_read) {
+ *error_is_read = true;
+ }
+ goto fail;
}
- goto fail;
- }
- ret = blk_co_pwrite(job->target, start, nbytes, *bounce_buffer,
- job->write_flags);
- if (ret < 0) {
- trace_backup_do_cow_write_fail(job, start, ret);
- if (error_is_read) {
- *error_is_read = false;
+ ret = blk_co_pwrite(job->target, start, chunk, bounce_buffer,
+ job->write_flags);
+ if (ret < 0) {
+ trace_backup_do_cow_write_fail(job, start, ret);
+ if (error_is_read) {
+ *error_is_read = false;
+ }
+ goto fail;
}
- goto fail;
+
+ start += chunk;
+ remaining_bytes -= chunk;
}
return nbytes;
@@ -301,9 +313,14 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
}
}
if (!job->use_copy_range) {
+ if (!bounce_buffer) {
+ size_t len = MIN(BACKUP_MAX_BOUNCE_BUFFER,
+ MAX(dirty_end - start, end - dirty_end));
+ bounce_buffer = blk_try_blockalign(job->common.blk, len);
+ }
ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
is_write_notifier,
- error_is_read, &bounce_buffer);
+ error_is_read, bounce_buffer);
}
if (ret < 0) {
break;
--
2.18.0
