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thp: copy_huge_pmd(): copy huge zero page 

It's easy to copy huge zero page. Just set destination pmd to huge zero
page.

It's safe to copy huge zero page since we have none yet :-p

[rientjes@google.com: fix comment]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Kirill A. Shutemov 2012-12-12 13:50:51 -08:00 committed by Linus Torvalds
parent 479f0abbfd
commit fc9fe822f7
1 changed files with 22 additions and 0 deletions
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22
mm/huge_memory.c
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@ -708,6 +708,18 @@ static inline struct page *alloc_hugepage(int defrag)
}
#endif
static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd)
{
pmd_t entry;
entry = pfn_pmd(huge_zero_pfn, vma->vm_page_prot);
entry = pmd_wrprotect(entry);
entry = pmd_mkhuge(entry);
set_pmd_at(mm, haddr, pmd, entry);
pgtable_trans_huge_deposit(mm, pgtable);
mm->nr_ptes++;
}
int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd,
unsigned int flags)
@ -785,6 +797,16 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
pte_free(dst_mm, pgtable);
goto out_unlock;
}
/*
* mm->page_table_lock is enough to be sure that huge zero pmd is not
* under splitting since we don't split the page itself, only pmd to
* a page table.
*/
if (is_huge_zero_pmd(pmd)) {
set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd);
ret = 0;
goto out_unlock;
}
if (unlikely(pmd_trans_splitting(pmd))) {
/* split huge page running from under us */
spin_unlock(&src_mm->page_table_lock);