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Subject: Re: [PATCH v4 02/23] mm/gup: factor out duplicate code from four
 routines
To:     Jan Kara <jack@suse.cz>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
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References: <20191113042710.3997854-1-jhubbard@nvidia.com>
 <20191113042710.3997854-3-jhubbard@nvidia.com>
 <20191113111521.GI6367@quack2.suse.cz>
From:   John Hubbard <jhubbard@nvidia.com>
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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: J=C3=A9r=C3=B4me 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>
>=20
>> 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
>>  =20
>> +static int __record_subpages(struct page *page, unsigned long addr,
>> +			     unsigned long end, struct page **pages, int nr)
>> +{
>> +	int nr_recorded_pages =3D 0;
>> +
>> +	do {
>> +		pages[nr] =3D page;
>> +		nr++;
>> +		page++;
>> +		nr_recorded_pages++;
>> +	} while (addr +=3D PAGE_SIZE, addr !=3D end);
>> +	return nr_recorded_pages;
>> +}
>=20
> 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, in=
t *nr)
>> +{
>> +	*nr +=3D nr_recorded_pages;
>> +	SetPageReferenced(head);
>> +}
>=20
> 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 accura=
tely
name should have been a big hint to not do it. I'll remove the helper and
put the lines back in directly.


thanks,
--=20
John Hubbard
NVIDIA

>=20
> Other than that the cleanup looks nice to me.
>=20
> 								Honza
>=20