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thp: lazy huge zero page allocation 

Instead of allocating huge zero page on hugepage_init() we can postpone it
until first huge zero page map. It saves memory if THP is not in use.

cmpxchg() is used to avoid race on huge_zero_pfn initialization.

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>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2012-12-12 13:51:05 -08:00 committed by Linus Torvalds
parent 80371957f0
commit 78ca0e6792
1 changed files with 10 additions and 10 deletions
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20
mm/huge_memory.c
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@ -160,22 +160,24 @@ static int start_khugepaged(void)
return err;
}
static int __init init_huge_zero_page(void)
static int init_huge_zero_pfn(void)
{
struct page *hpage;
unsigned long pfn;
hpage = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
HPAGE_PMD_ORDER);
if (!hpage)
return -ENOMEM;
huge_zero_pfn = page_to_pfn(hpage);
pfn = page_to_pfn(hpage);
if (cmpxchg(&huge_zero_pfn, 0, pfn))
__free_page(hpage);
return 0;
}
static inline bool is_huge_zero_pfn(unsigned long pfn)
{
return pfn == huge_zero_pfn;
return huge_zero_pfn && pfn == huge_zero_pfn;
}
static inline bool is_huge_zero_pmd(pmd_t pmd)
@ -564,10 +566,6 @@ static int __init hugepage_init(void)
if (err)
return err;
err = init_huge_zero_page();
if (err)
goto out;
err = khugepaged_slab_init();
if (err)
goto out;
@ -590,8 +588,6 @@ static int __init hugepage_init(void)
return 0;
out:
if (huge_zero_pfn)
__free_page(pfn_to_page(huge_zero_pfn));
hugepage_exit_sysfs(hugepage_kobj);
return err;
}
@ -735,6 +731,10 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
return VM_FAULT_OOM;
if (!(flags & FAULT_FLAG_WRITE)) {
pgtable_t pgtable;
if (unlikely(!huge_zero_pfn && init_huge_zero_pfn())) {
count_vm_event(THP_FAULT_FALLBACK);
goto out;
}
pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable))
return VM_FAULT_OOM;