linux-kernel - Re: [PATCH 3/4] mm/gup: add a range variant of unpin_user_pages_dirty

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Date:   Wed, 3 Feb 2021 16:11:01 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Joao Martins <joao.m.martins@...cle.com>, <linux-mm@...ck.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Doug Ledford <dledford@...hat.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 3/4] mm/gup: add a range variant of
 unpin_user_pages_dirty_lock()

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