Re: [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines

[John Hubbard]

On 11/13/19 3:15 AM, Jan Kara wrote:
> On Tue 12-11-19 20:26:49, 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: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> > 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>
>
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 85caf76b3012..199da99e8ffc 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1969,6 +1969,34 @@ 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)
> > +{
> > +	int nr_recorded_pages = 0;
> > +
> > +	do {
> > +		pages[nr] = page;
> > +		nr++;
> > +		page++;
> > +		nr_recorded_pages++;
> > +	} while (addr += PAGE_SIZE, addr != end);
> > +	return nr_recorded_pages;
> > +}
>
> Why don't you pass in already pages + nr?

Aha, that does save a function argument. Will do.

...
> > +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
> > +{
> > +	*nr += nr_recorded_pages;
> > +	SetPageReferenced(head);
> > +}
>
> I don't find this last helper very useful. It seems to muddy water more
> than necessary...

Yes, I suspect it's rather unloved, and the fact that it was hard to accurately
name should have been a big hint to not do it. I'll remove the helper and
put the lines back in directly.


thanks,
--
John Hubbard
NVIDIA

> Other than that the cleanup looks nice to me.
>
> 								Honza