Re: [Qemu-devel] [PATCH v3 8/9] Use qemu_put_buffer_no_copy for guest memory pages

[Juan Quintela <quintela@redhat.com>]

Orit Wasserman <owasserm@redhat.com> wrote:
> This will remove an unneeded copy of guest memory pages.
> For the page header and device state we still copy the data to the
> static buffer the other option is to allocate the memory on demand
> which is more expensive.
>
> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
> ---
>  arch_init.c | 2 +-
>  savevm.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index 98e2bc6..27b53eb 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -481,7 +481,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
>              /* XBZRLE overflow or normal page */
>              if (bytes_sent == -1) {
>                  bytes_sent = save_block_hdr(f, block, offset, cont, RAM_SAVE_FLAG_PAGE);
> -                qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> +                qemu_put_buffer_no_copy(f, p, TARGET_PAGE_SIZE);
>                  bytes_sent += TARGET_PAGE_SIZE;
>                  acct_info.norm_pages++;
>              }

Once here, shouldn't we also change:

block-migration.c::blk_send()

    qemu_put_buffer(f, blk->buf, BLOCK_SIZE);

to nocopy?

Again, this can be an additional patch.


> diff --git a/savevm.c b/savevm.c
> index fbfb9e3..50e8fb2 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -634,7 +634,7 @@ void qemu_put_buffer_no_copy(QEMUFile *f, const uint8_t *buf, int size)
>          abort();
>      }
>  
> -    f->iov[f->iovcnt].iov_base = f->buf + f->buf_index;
> +    f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
>      f->iov[f->iovcnt++].iov_len = size;

This bit should be in the previous patch, the error that I pointed?

Later, Juan.