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@xxxxxxxxx> 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@xxxxxxxxx>
> > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Dimitri Sivanich <sivanich@xxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: linux-mm@xxxxxxxxx
> > Signed-off-by: Bharath Vedartham <linux.bhar@xxxxxxxxx>
> > ---
> > 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
> >
>
