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Date: Mon, 4 Nov 2019 11:51:18 -0500
From: Jerome Glisse <jglisse@redhat.com>
To: John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v2 02/18] mm/gup: factor out duplicate code from four
 routines
Message-ID: <20191104165118.GB5134@redhat.com>
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On Sun, Nov 03, 2019 at 01:17:57PM -0800, 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.
>=20
> Factor out the common code into static functions, thus reducing the
> overall line count and the code's complexity.
>=20
> 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().
>=20
> Also, further simplify (slightly), by waiting until the the successful
> end of each routine, to increment *nr.
>=20
> 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>

Good cleanup.

Reviewed-by: J=E9r=F4me Glisse <jglisse@redhat.com>

> ---
>  mm/gup.c | 104 ++++++++++++++++++++++++-------------------------------
>  1 file changed, 45 insertions(+), 59 deletions(-)
>=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,
> +=09=09=09     unsigned long end, struct page **pages, int nr)
> +{
> +=09int nr_recorded_pages =3D 0;
> +
> +=09do {
> +=09=09pages[nr] =3D page;
> +=09=09nr++;
> +=09=09page++;
> +=09=09nr_recorded_pages++;
> +=09} while (addr +=3D PAGE_SIZE, addr !=3D end);
> +=09return nr_recorded_pages;
> +}
> +
> +static void put_compound_head(struct page *page, int refs)
> +{
> +=09/* Do a get_page() first, in case refs =3D=3D page->_refcount */
> +=09get_page(page);
> +=09page_ref_sub(page, refs);
> +=09put_page(page);
> +}
> +
> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int=
 *nr)
> +{
> +=09*nr +=3D nr_recorded_pages;
> +=09SetPageReferenced(head);
> +}
> +
>  #ifdef CONFIG_ARCH_HAS_HUGEPD
>  static unsigned long hugepte_addr_end(unsigned long addr, unsigned long =
end,
>  =09=09=09=09      unsigned long sz)
> @@ -1998,33 +2026,20 @@ static int gup_hugepte(pte_t *ptep, unsigned long=
 sz, unsigned long addr,
>  =09/* hugepages are never "special" */
>  =09VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
> =20
> -=09refs =3D 0;
>  =09head =3D pte_page(pte);
> -
>  =09page =3D head + ((addr & (sz-1)) >> PAGE_SHIFT);
> -=09do {
> -=09=09VM_BUG_ON(compound_head(page) !=3D head);
> -=09=09pages[*nr] =3D page;
> -=09=09(*nr)++;
> -=09=09page++;
> -=09=09refs++;
> -=09} while (addr +=3D PAGE_SIZE, addr !=3D end);
> +=09refs =3D __record_subpages(page, addr, end, pages, *nr);
> =20
>  =09head =3D try_get_compound_head(head, refs);
> -=09if (!head) {
> -=09=09*nr -=3D refs;
> +=09if (!head)
>  =09=09return 0;
> -=09}
> =20
>  =09if (unlikely(pte_val(pte) !=3D pte_val(*ptep))) {
> -=09=09/* Could be optimized better */
> -=09=09*nr -=3D refs;
> -=09=09while (refs--)
> -=09=09=09put_page(head);
> +=09=09put_compound_head(head, refs);
>  =09=09return 0;
>  =09}
> =20
> -=09SetPageReferenced(head);
> +=09__huge_pt_done(head, refs, nr);
>  =09return 1;
>  }
> =20
> @@ -2071,29 +2086,19 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, =
unsigned long addr,
>  =09=09=09=09=09     pages, nr);
>  =09}
> =20
> -=09refs =3D 0;
>  =09page =3D pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> -=09do {
> -=09=09pages[*nr] =3D page;
> -=09=09(*nr)++;
> -=09=09page++;
> -=09=09refs++;
> -=09} while (addr +=3D PAGE_SIZE, addr !=3D end);
> +=09refs =3D __record_subpages(page, addr, end, pages, *nr);
> =20
>  =09head =3D try_get_compound_head(pmd_page(orig), refs);
> -=09if (!head) {
> -=09=09*nr -=3D refs;
> +=09if (!head)
>  =09=09return 0;
> -=09}
> =20
>  =09if (unlikely(pmd_val(orig) !=3D pmd_val(*pmdp))) {
> -=09=09*nr -=3D refs;
> -=09=09while (refs--)
> -=09=09=09put_page(head);
> +=09=09put_compound_head(head, refs);
>  =09=09return 0;
>  =09}
> =20
> -=09SetPageReferenced(head);
> +=09__huge_pt_done(head, refs, nr);
>  =09return 1;
>  }
> =20
> @@ -2114,29 +2119,19 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, =
unsigned long addr,
>  =09=09=09=09=09     pages, nr);
>  =09}
> =20
> -=09refs =3D 0;
>  =09page =3D pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> -=09do {
> -=09=09pages[*nr] =3D page;
> -=09=09(*nr)++;
> -=09=09page++;
> -=09=09refs++;
> -=09} while (addr +=3D PAGE_SIZE, addr !=3D end);
> +=09refs =3D __record_subpages(page, addr, end, pages, *nr);
> =20
>  =09head =3D try_get_compound_head(pud_page(orig), refs);
> -=09if (!head) {
> -=09=09*nr -=3D refs;
> +=09if (!head)
>  =09=09return 0;
> -=09}
> =20
>  =09if (unlikely(pud_val(orig) !=3D pud_val(*pudp))) {
> -=09=09*nr -=3D refs;
> -=09=09while (refs--)
> -=09=09=09put_page(head);
> +=09=09put_compound_head(head, refs);
>  =09=09return 0;
>  =09}
> =20
> -=09SetPageReferenced(head);
> +=09__huge_pt_done(head, refs, nr);
>  =09return 1;
>  }
> =20
> @@ -2151,29 +2146,20 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, =
unsigned long addr,
>  =09=09return 0;
> =20
>  =09BUILD_BUG_ON(pgd_devmap(orig));
> -=09refs =3D 0;
> +
>  =09page =3D pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
> -=09do {
> -=09=09pages[*nr] =3D page;
> -=09=09(*nr)++;
> -=09=09page++;
> -=09=09refs++;
> -=09} while (addr +=3D PAGE_SIZE, addr !=3D end);
> +=09refs =3D __record_subpages(page, addr, end, pages, *nr);
> =20
>  =09head =3D try_get_compound_head(pgd_page(orig), refs);
> -=09if (!head) {
> -=09=09*nr -=3D refs;
> +=09if (!head)
>  =09=09return 0;
> -=09}
> =20
>  =09if (unlikely(pgd_val(orig) !=3D pgd_val(*pgdp))) {
> -=09=09*nr -=3D refs;
> -=09=09while (refs--)
> -=09=09=09put_page(head);
> +=09=09put_compound_head(head, refs);
>  =09=09return 0;
>  =09}
> =20
> -=09SetPageReferenced(head);
> +=09__huge_pt_done(head, refs, nr);
>  =09return 1;
>  }
> =20
> --=20
> 2.23.0
>=20