> On 03/16/2017 05:45 PM, Balbir Singh wrote:
> > On Fri, Mar 17, 2017 at 11:22 AM, John Hubbard <jhubbard@xxxxxxxxxx> wrote:
> >> On 03/16/2017 04:05 PM, Andrew Morton wrote:
> >>>
> >>> On Thu, 16 Mar 2017 12:05:26 -0400 Jérôme Glisse <jglisse@xxxxxxxxxx>
> >>> wrote:
> >>>
> >>>> +static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
> >>>> +{
> >>>> + if (!(mpfn & MIGRATE_PFN_VALID))
> >>>> + return NULL;
> >>>> + return pfn_to_page(mpfn & MIGRATE_PFN_MASK);
> >>>> +}
> >>>
> >>>
> >>> i386 allnoconfig:
> >>>
> >>> In file included from mm/page_alloc.c:61:
> >>> ./include/linux/migrate.h: In function 'migrate_pfn_to_page':
> >>> ./include/linux/migrate.h:139: warning: left shift count >= width of type
> >>> ./include/linux/migrate.h:141: warning: left shift count >= width of type
> >>> ./include/linux/migrate.h: In function 'migrate_pfn_size':
> >>> ./include/linux/migrate.h:146: warning: left shift count >= width of type
> >>>
> >>
> >> It seems clear that this was never meant to work with < 64-bit pfns:
> >>
> >> // migrate.h excerpt:
> >> #define MIGRATE_PFN_VALID (1UL << (BITS_PER_LONG_LONG - 1))
> >> #define MIGRATE_PFN_MIGRATE (1UL << (BITS_PER_LONG_LONG - 2))
> >> #define MIGRATE_PFN_HUGE (1UL << (BITS_PER_LONG_LONG - 3))
> >> #define MIGRATE_PFN_LOCKED (1UL << (BITS_PER_LONG_LONG - 4))
> >> #define MIGRATE_PFN_WRITE (1UL << (BITS_PER_LONG_LONG - 5))
> >> #define MIGRATE_PFN_DEVICE (1UL << (BITS_PER_LONG_LONG - 6))
> >> #define MIGRATE_PFN_ERROR (1UL << (BITS_PER_LONG_LONG - 7))
> >> #define MIGRATE_PFN_MASK ((1UL << (BITS_PER_LONG_LONG -
> >> PAGE_SHIFT))
> >> - 1)
> >>
> >> ...obviously, there is not enough room for these flags, in a 32-bit pfn.
> >>
> >> So, given the current HMM design, I think we are going to have to provide
> >> a
> >> 32-bit version of these routines (migrate_pfn_to_page, and related) that
> >> is
> >> a no-op, right?
> >
> > Or make the HMM Kconfig feature 64BIT only by making it depend on 64BIT?
> >
>
> Yes, that was my first reaction too, but these particular routines are
> aspiring to be generic
> routines--in fact, you have had an influence there, because these might
> possibly help with NUMA
> migrations. :)
>
> So it would look odd to see this:
>
> #ifdef CONFIG_HMM
> int migrate_vma(const struct migrate_vma_ops *ops,
> struct vm_area_struct *vma,
> unsigned long mentries,
> unsigned long start,
> unsigned long end,
> unsigned long *src,
> unsigned long *dst,
> void *private)
> {
> //...implementation
> #endif
>
> ...because migrate_vma() does not sound HMM-specific, and it is, after all,
> in migrate.h and
> migrate.c. We probably want this a more generic approach (not sure if I've
> picked exactly the right
> token to #ifdef on, but it's close):
>
> #ifdef CONFIG_64BIT
> int migrate_vma(const struct migrate_vma_ops *ops,
> struct vm_area_struct *vma,
> unsigned long mentries,
> unsigned long start,
> unsigned long end,
> unsigned long *src,
> unsigned long *dst,
> void *private)
> {
> /* ... full implementation */
> }
>
> #else
> int migrate_vma(const struct migrate_vma_ops *ops,
> struct vm_area_struct *vma,
> unsigned long mentries,
> unsigned long start,
> unsigned long end,
> unsigned long *src,
> unsigned long *dst,
> void *private)
> {
> return -EINVAL; /* or something more appropriate */
> }
> #endif
>
> thanks
> John Hubbard
> NVIDIA
The original intention was for it to be 64bit only, 32bit is a dying
species and before splitting out hmm_ prefix from this code and moving
it to be generic it was behind a 64bit flag.
If latter one someone really care about 32bit we can only move to u64
Cheers,
Jérôme
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