From: Bharath Vedartham <linux.bhar@gmail.com>
To: William Kucharski <william.kucharski@oracle.com>
Cc: arnd@arndb.de, sivanich@sgi.com, gregkh@linuxfoundation.org,
ira.weiny@intel.com, jhubbard@nvidia.com, jglisse@redhat.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/3] sgi-gru: Remove CONFIG_HUGETLB_PAGE ifdef
Date: Mon, 22 Jul 2019 23:20:22 +0530 [thread overview]
Message-ID: <20190722175022.GB12278@bharath12345-Inspiron-5559> (raw)
In-Reply-To: <1BA84A99-4EB5-4520-BFBD-CD60D5B7AED9@oracle.com>
On Sun, Jul 21, 2019 at 09:20:38PM -0600, William Kucharski wrote:
> I suspect I'm being massively pedantic here, but the comments for atomic_pte_lookup() note:
>
> * Only supports Intel large pages (2MB only) on x86_64.
> * ZZZ - hugepage support is incomplete
>
> That makes me wonder how many systems using this hardware are actually configured with CONFIG_HUGETLB_PAGE.
>
> I ask as in the most common case, this is likely introducing a few extra instructions and possibly an additional branch to a routine that is called per-fault.
>
> So the nit-picky questions are:
>
> 1) Does the code really need to be cleaned up in this way?
>
> 2) If it does, does it make more sense (given the way pmd_large() is handled now in atomic_pte_lookup()) for this to be coded as:
>
> if (unlikely(is_vm_hugetlb_page(vma)))
> *pageshift = HPAGE_SHIFT;
> else
> *pageshift = PAGE_SHIFT;
>
> In all likelihood, these questions are no-ops, and the optimizer may even make my questions completely moot, but I thought I might as well ask anyway.
>
That sounds reasonable. I am not really sure as to how much of
an improvement it would be, the condition will be evaluated eitherways
AFAIK? Eitherways, the ternary operator does not look good. I ll make a
version 2 of this.
> > On Jul 21, 2019, at 9:58 AM, Bharath Vedartham <linux.bhar@gmail.com> wrote:
> >
> > is_vm_hugetlb_page has checks for whether CONFIG_HUGETLB_PAGE is defined
> > or not. If CONFIG_HUGETLB_PAGE is not defined is_vm_hugetlb_page will
> > always return false. There is no need to have an uneccessary
> > CONFIG_HUGETLB_PAGE check in the code.
> >
> > 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 | 11 +++--------
> > 1 file changed, 3 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> > index 61b3447..75108d2 100644
> > --- a/drivers/misc/sgi-gru/grufault.c
> > +++ b/drivers/misc/sgi-gru/grufault.c
> > @@ -180,11 +180,8 @@ static int non_atomic_pte_lookup(struct vm_area_struct *vma,
> > {
> > struct page *page;
> >
> > -#ifdef CONFIG_HUGETLB_PAGE
> > *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> > -#else
> > - *pageshift = PAGE_SHIFT;
> > -#endif
> > +
> > if (get_user_pages(vaddr, 1, write ? FOLL_WRITE : 0, &page, NULL) <= 0)
> > return -EFAULT;
> > *paddr = page_to_phys(page);
> > @@ -238,11 +235,9 @@ static int atomic_pte_lookup(struct vm_area_struct *vma, unsigned long vaddr,
> > return 1;
> >
> > *paddr = pte_pfn(pte) << PAGE_SHIFT;
> > -#ifdef CONFIG_HUGETLB_PAGE
> > +
> > *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
> > -#else
> > - *pageshift = PAGE_SHIFT;
> > -#endif
> > +
> > return 0;
> >
> > err:
> > --
> > 2.7.4
> >
>
next prev parent reply other threads:[~2019-07-22 17:50 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 [this message]
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
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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