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mm, thp: fix collapsing of hugepages on madvise

If an anonymous mapping is not allowed to fault thp memory and then madvise(MADV_HUGEPAGE) is used after fault, khugepaged will never collapse this memory into thp memory. This occurs because the madvise(2) handler for thp, hugepage_madvise(), clears VM_NOHUGEPAGE on the stack and it isn't stored in vma->vm_flags until the final action of madvise_behavior(). This causes the khugepaged_enter_vma_merge() to be a no-op in hugepage_madvise() when the vma had previously had VM_NOHUGEPAGE set. Fix this by passing the correct vma flags to the khugepaged mm slot handler. There's no chance khugepaged can run on this vma until after madvise_behavior() returns since we hold mm->mmap_sem. It would be possible to clear VM_NOHUGEPAGE directly from vma->vm_flags in hugepage_advise(), but I didn't want to introduce special case behavior into madvise_behavior(). I think it's best to just let it always set vma->vm_flags itself.

David Rientjes committed 12 years ago

Commit 6d50e601 parent 47f29df3 files · +20 −16Browse files

Showing the changes to include/linux (1 of 3 files). Show all

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include/linux/khugepaged.h+10−7
@@ -6,7 +6,8 @@ · 5 unmodified lines
6#ifdef CONFIG_TRANSPARENT_HUGEPAGE6#ifdef CONFIG_TRANSPARENT_HUGEPAGE
7extern int __khugepaged_enter(struct mm_struct *mm);7extern int __khugepaged_enter(struct mm_struct *mm);
8extern void __khugepaged_exit(struct mm_struct *mm);8extern void __khugepaged_exit(struct mm_struct *mm);
9extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma);9extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
10 unsigned long vm_flags);
10 11
11#define khugepaged_enabled() \12#define khugepaged_enabled() \
12 (transparent_hugepage_flags & \13 (transparent_hugepage_flags & \
@@ -35,13 +36,13 @@ static inline void khugepaged_exit(struct mm_struct *mm) · 22 unmodified lines
35 __khugepaged_exit(mm);36 __khugepaged_exit(mm);
36}37}
37 38
38static inline int khugepaged_enter(struct vm_area_struct *vma)39static inline int khugepaged_enter(struct vm_area_struct *vma,
40 unsigned long vm_flags)
39{41{
40 if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))42 if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
41 if ((khugepaged_always() ||43 if ((khugepaged_always() ||
42 (khugepaged_req_madv() &&44 (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
43 vma->vm_flags & VM_HUGEPAGE)) &&45 !(vm_flags & VM_NOHUGEPAGE))
44 !(vma->vm_flags & VM_NOHUGEPAGE))
45 if (__khugepaged_enter(vma->vm_mm))46 if (__khugepaged_enter(vma->vm_mm))
46 return -ENOMEM;47 return -ENOMEM;
47 return 0;48 return 0;
@@ -54,11 +55,13 @@ static inline int khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm) · 6 unmodified lines
54static inline void khugepaged_exit(struct mm_struct *mm)55static inline void khugepaged_exit(struct mm_struct *mm)
55{56{
56}57}
57static inline int khugepaged_enter(struct vm_area_struct *vma)58static inline int khugepaged_enter(struct vm_area_struct *vma,
59 unsigned long vm_flags)
58{60{
59 return 0;61 return 0;
60}62}
61static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma)63static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
64 unsigned long vm_flags)
62{65{
63 return 0;66 return 0;
64}67}