Re: [PATCH v5 02/24] mm/gup: factor out duplicate code from four routines

[Jan Kara]

On Thu 14-11-19 21:53:18, John Hubbard wrote:
> There are four locations in gup.c that have a fair amount of code
> duplication. This means that changing one requires making the same
> changes in four places, not to mention reading the same code four
> times, and wondering if there are subtle differences.
> 
> Factor out the common code into static functions, thus reducing the
> overall line count and the code's complexity.
> 
> Also, take the opportunity to slightly improve the efficiency of the
> error cases, by doing a mass subtraction of the refcount, surrounded
> by get_page()/put_page().
> 
> Also, further simplify (slightly), by waiting until the the successful
> end of each routine, to increment *nr.
> 
> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
>  mm/gup.c | 95 ++++++++++++++++++++++++--------------------------------
>  1 file changed, 40 insertions(+), 55 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 85caf76b3012..858541ea30ce 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1969,6 +1969,29 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
>  }
>  #endif
>  
> +static int __record_subpages(struct page *page, unsigned long addr,
> +			     unsigned long end, struct page **pages)
> +{
> +	int nr = 0;
> +	int nr_recorded_pages = 0;
> +
> +	do {
> +		pages[nr] = page;
> +		nr++;
> +		page++;
> +		nr_recorded_pages++;
> +	} while (addr += PAGE_SIZE, addr != end);
> +	return nr_recorded_pages;

nr == nr_recorded_pages so no need for both... BTW, structuring this as a
for loop would be probably more logical and shorter now:

	for (nr = 0; addr != end; addr += PAGE_SIZE)
		pages[nr++] = page++;
	return nr;

The rest of the patch looks good to me.

								Honza

-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR