Commit 2275cc90 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Stefan Hajnoczi
Browse files

block/io: bdrv_co_do_copy_on_readv: lazy allocation 



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

Signed-off-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190604161514.262241-7-vsementsov@virtuozzo.com
Message-Id: <20190604161514.262241-7-vsementsov@virtuozzo.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 1143ec5e

block/io.c

+12 −9
Original line number Diff line number Diff line
@@ -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,