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Commit 78ca0e67 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

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: default avatarKirill 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 80371957

mm/huge_memory.c

+10 −10
Original line number Diff line number Diff line
@@ -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;