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SubjectRe: [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines
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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: Jérôme Glisse <jglisse@redhat.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>
>> 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
>

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