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
Balbir Singh
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