On 04/07/2016 02:34 PM, Balbir Singh wrote:
>
>
> On 07/04/16 15:37, Anshuman Khandual wrote:
>> Currently the config ARCH_WANT_GENERAL_HUGETLB enabled functions like
>> 'huge_pte_alloc' and 'huge_pte_offset' dont take into account HugeTLB
>> page implementation at the PGD level. This is also true for functions
>> like 'follow_page_mask' which is called from move_pages() system call.
>> This lack of PGD level huge page support prohibits some architectures
>> to use these generic HugeTLB functions.
>>
>
> From what I know of move_pages(), it will always call follow_page_mask()
> with FOLL_GET (I could be wrong here) and the implementation below
> returns NULL for follow_huge_pgd().
You are right. This patch makes ARCH_WANT_GENERAL_HUGETLB functions aware
of PGD implementation so that we can do all transactions on 16GB pages
using these function instead of the present arch overrides. But that also
requires follow_page_mask() changes for every other access to the page
than the migrate_pages() usage.
But yes, we dont support migrate_pages() on PGD based pages yet, hence
it just returns NULL in that case. May be the commit message needs to
reflect this.
>
>> This change adds the required PGD based implementation awareness and
>> with that, more architectures like POWER which implements 16GB pages
>> at the PGD level along with the 16MB pages at the PMD level can now
>> use ARCH_WANT_GENERAL_HUGETLB config option.
>>
>> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
>> ---
>> include/linux/hugetlb.h | 3 +++
>> mm/gup.c | 6 ++++++
>> mm/hugetlb.c | 20 ++++++++++++++++++++
>> 3 files changed, 29 insertions(+)
>>
>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>> index 7d953c2..71832e1 100644
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -115,6 +115,8 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
>> pmd_t *pmd, int flags);
>> struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
>> pud_t *pud, int flags);
>> +struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
>> + pgd_t *pgd, int flags);
>> int pmd_huge(pmd_t pmd);
>> int pud_huge(pud_t pmd);
>> unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
>> @@ -143,6 +145,7 @@ static inline void hugetlb_show_meminfo(void)
>> }
>> #define follow_huge_pmd(mm, addr, pmd, flags) NULL
>> #define follow_huge_pud(mm, addr, pud, flags) NULL
>> +#define follow_huge_pgd(mm, addr, pgd, flags) NULL
>> #define prepare_hugepage_range(file, addr, len) (-EINVAL)
>> #define pmd_huge(x) 0
>> #define pud_huge(x) 0
>> diff --git a/mm/gup.c b/mm/gup.c
>> index fb87aea..9bac78c 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -234,6 +234,12 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
>> pgd = pgd_offset(mm, address);
>> if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
>> return no_page_table(vma, flags);
>> + if (pgd_huge(*pgd) && vma->vm_flags & VM_HUGETLB) {
>> + page = follow_huge_pgd(mm, address, pgd, flags);
>> + if (page)
>> + return page;
>> + return no_page_table(vma, flags);
> This will return NULL as well?
That right, no_page_table() returns NULL for FOLL_GET when we fall through
after failing on follow_huge_pgd().
>> + }
>>
>> pud = pud_offset(pgd, address);
>> if (pud_none(*pud))
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 19d0d08..5ea3158 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -4250,6 +4250,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
>> pte_t *pte = NULL;
>>
>> pgd = pgd_offset(mm, addr);
>> + if (sz == PGDIR_SIZE) {
>> + pte = (pte_t *)pgd;
>> + goto huge_pgd;
>> + }
>> +
>
> No allocation for a pgd slot - right?
No, its already allocated for the mm during creation.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>