On Mon, Jan 21, 2013 at 04:05:27PM +0800, Asias He wrote:
> We can get all the pages in one time instead of calling
> gup N times.
>
> Signed-off-by: Asias He <asias@xxxxxxxxxx>
> ---
> drivers/vhost/tcm_vhost.c | 33 ++++++++++++++++++++-------------
> 1 file changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index ca35c16..59be442 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -430,37 +430,45 @@ static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
> * Returns the number of scatterlist entries used or -errno on error.
> */
> static int vhost_scsi_map_to_sgl(struct scatterlist *sgl,
> - unsigned int sgl_count, void __user *ptr, size_t len, int write)
> + unsigned int sgl_count, struct iovec *iov, int write)
> {
> struct scatterlist *sg = sgl;
> unsigned int npages = 0;
> + void __user *ptr = iov->iov_base;
> + size_t len = iov->iov_len;
> int ret;
> + unsigned int pages_nr, offset, nbytes;
> + struct page **pages;
> +
> + pages_nr = iov_num_pages(iov);
> + pages = kmalloc(pages_nr * sizeof(struct page *), GFP_ATOMIC);
> + if (!pages)
> + return -ENOMEM;
> +
> + ret = get_user_pages_fast((unsigned long)ptr, pages_nr, write, pages);
> + if (ret != pages_nr)
> + goto err;
1. Why GFP_ATOMIC? get_user_pages_fast can sleep, so this path must not
be atomic (if it is, should use __get_user_pages_fast).
GFP_ATOMIC should be avoided.
2. Should drop reference to pages whose refcount has been increased,
if ret > 0 && ret != pages_nr (see last phrase of get_user_pages_fast
commentary).
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