From: John Hubbard <jhubbard@nvidia.com>
To: Bharath Vedartham <linux.bhar@gmail.com>, <arnd@arndb.de>,
<sivanich@sgi.com>, <gregkh@linuxfoundation.org>
Cc: <ira.weiny@intel.com>, <jglisse@redhat.com>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] sgi-gru: Use __get_user_pages_fast in atomic_pte_lookup
Date: Sun, 21 Jul 2019 19:32:36 -0700 [thread overview]
Message-ID: <c508330d-a5d0-fba3-9dd0-eb820a96ee09@nvidia.com> (raw)
In-Reply-To: <1563724685-6540-4-git-send-email-linux.bhar@gmail.com>
On 7/21/19 8:58 AM, Bharath Vedartham wrote:
> *pte_lookup functions get the physical address for a given virtual
> address by getting a physical page using gup and use page_to_phys to get
> the physical address.
>
> Currently, atomic_pte_lookup manually walks the page tables. If this
> function fails to get a physical page, it will fall back too
> non_atomic_pte_lookup to get a physical page which uses the slow gup
> path to get the physical page.
>
> Instead of manually walking the page tables use __get_user_pages_fast
> which does the same thing and it does not fall back to the slow gup
> path.
>
> This is largely inspired from kvm code. kvm uses __get_user_pages_fast
> in hva_to_pfn_fast function which can run in an atomic context.
>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Dimitri Sivanich <sivanich@sgi.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org
> Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> ---
> drivers/misc/sgi-gru/grufault.c | 39 +++++----------------------------------
> 1 file changed, 5 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index 75108d2..121c9a4 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -202,46 +202,17 @@ static int non_atomic_pte_lookup(struct vm_area_struct *vma,
> static int atomic_pte_lookup(struct vm_area_struct *vma, unsigned long vaddr,
> int write, unsigned long *paddr, int *pageshift)
> {
> - pgd_t *pgdp;
> - p4d_t *p4dp;
> - pud_t *pudp;
> - pmd_t *pmdp;
> - pte_t pte;
> -
> - pgdp = pgd_offset(vma->vm_mm, vaddr);
> - if (unlikely(pgd_none(*pgdp)))
> - goto err;
> -
> - p4dp = p4d_offset(pgdp, vaddr);
> - if (unlikely(p4d_none(*p4dp)))
> - goto err;
> -
> - pudp = pud_offset(p4dp, vaddr);
> - if (unlikely(pud_none(*pudp)))
> - goto err;
> + struct page *page;
>
> - pmdp = pmd_offset(pudp, vaddr);
> - if (unlikely(pmd_none(*pmdp)))
> - goto err;
> -#ifdef CONFIG_X86_64
> - if (unlikely(pmd_large(*pmdp)))
> - pte = *(pte_t *) pmdp;
> - else
> -#endif
> - pte = *pte_offset_kernel(pmdp, vaddr);
> + *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
>
> - if (unlikely(!pte_present(pte) ||
> - (write && (!pte_write(pte) || !pte_dirty(pte)))))
> + if (!__get_user_pages_fast(vaddr, 1, write, &page))
> return 1;
Let's please use numeric, not boolean comparison, for the return value of
gup.
Also, optional: as long as you're there, atomic_pte_lookup() ought to
either return a bool (true == success) or an errno, rather than a
numeric zero or one.
Other than that, this looks like a good cleanup, I wonder how many
open-coded gup implementations are floating around like this.
thanks,
--
John Hubbard
NVIDIA
>
> - *paddr = pte_pfn(pte) << PAGE_SHIFT;
> -
> - *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> + *paddr = page_to_phys(page);
> + put_user_page(page);
>
> return 0;
> -
> -err:
> - return 1;
> }
>
> static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>
next prev parent reply other threads:[~2019-07-22 2:32 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-21 15:58 [PATCH 0/3] sgi-gru: get_user_page changes Bharath Vedartham
2019-07-21 15:58 ` [PATCH 1/3] sgi-gru: Convert put_page() to get_user_page*() Bharath Vedartham
2019-07-22 2:25 ` John Hubbard
2019-07-22 17:47 ` Bharath Vedartham
2019-07-21 15:58 ` [PATCH 2/3] sgi-gru: Remove CONFIG_HUGETLB_PAGE ifdef Bharath Vedartham
2019-07-22 2:34 ` John Hubbard
2019-07-22 3:20 ` William Kucharski
2019-07-22 17:50 ` Bharath Vedartham
2019-07-22 22:53 ` William Kucharski
2019-07-21 15:58 ` [PATCH 3/3] sgi-gru: Use __get_user_pages_fast in atomic_pte_lookup Bharath Vedartham
2019-07-22 2:32 ` John Hubbard [this message]
2019-07-22 17:53 ` Bharath Vedartham
2019-07-22 23:06 ` John Hubbard
2019-07-22 4:49 ` [PATCH 0/3] sgi-gru: get_user_page changes Ira Weiny
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