Re: [PATCH 3/4] mm/gup: add a range variant of unpin_user_pages_dirty_lock()

[John Hubbard <jhubbard@nvidia.com>]

On 2/3/21 2:00 PM, Joao Martins wrote:
...
> +void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
> +				      bool make_dirty)
> +{
> +	unsigned long index;
> +	struct page *head;
> +	unsigned int ntails;
> +
> +	for_each_compound_range(index, &page, npages, head, ntails) {
> +		if (make_dirty && !PageDirty(head))
> +			set_page_dirty_lock(head);
> +		put_compound_head(head, ntails, FOLL_PIN);
> +	}
> +}
> +EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
> +

Also, looking at this again while trying to verify the sg diffs in patch #4, I noticed
that the name is tricky. Usually a "range" would not have a single struct page* as the
argument. So in this case, perhaps a comment above the function would help, something
approximately like this:

/*
  * The "range" in the function name refers to the fact that the page may be a
  * compound page. If so, then that compound page will be treated as one or more
  * ranges of contiguous tail pages.
  */

...I guess. Or maybe the name is just wrong (a comment block explaining a name is
always a bad sign). Perhaps we should rename it to something like:

	unpin_user_compound_page_dirty_lock()

?

thanks,
-- 
John Hubbard
NVIDIA