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SubjectRe: [RFC PATCH 1/2] vmsplice unmap gifted pages for recipient
On 07/25/2013 10:21 AM, Robert Jennings wrote:
> +static void zap_buf_page(unsigned long useraddr)
> +{
> + struct vm_area_struct *vma;
> +
> + down_read(&current->mm->mmap_sem);
> + vma = find_vma_intersection(current->mm, useraddr,
> + useraddr + PAGE_SIZE);
> + if (!IS_ERR_OR_NULL(vma))
> + zap_page_range(vma, useraddr, PAGE_SIZE, NULL);
> + up_read(&current->mm->mmap_sem);
> +}
> +
> /**
> * splice_to_pipe - fill passed data into a pipe
> * @pipe: pipe to fill
> @@ -212,8 +224,16 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
> buf->len = spd->partial[page_nr].len;
> buf->private = spd->partial[page_nr].private;
> buf->ops = spd->ops;
> - if (spd->flags & SPLICE_F_GIFT)
> + if (spd->flags & SPLICE_F_GIFT) {
> + unsigned long useraddr =
> + spd->partial[page_nr].useraddr;
> +
> + if ((spd->flags & SPLICE_F_MOVE) &&
> + !buf->offset && (buf->len == PAGE_SIZE))
> + /* Can move page aligned buf */
> + zap_buf_page(useraddr);
> buf->flags |= PIPE_BUF_FLAG_GIFT;
> + }

There isn't quite enough context here, but is it going to do this
zap_buf_page() very often? Seems a bit wasteful to do the up/down and
find_vma() every trip through the loop.


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