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    Subject[v3 PATCH 5/8] mm: khugepaged: make khugepaged_enter() void function
    Date
    The most callers of khugepaged_enter() don't care about the return
    value. Only dup_mmap(), anonymous THP page fault and MADV_HUGEPAGE handle
    the error by returning -ENOMEM. Actually it is not harmful for them to
    ignore the error case either. It also sounds overkilling to fail fork()
    and page fault early due to khugepaged_enter() error, and MADV_HUGEPAGE
    does set VM_HUGEPAGE flag regardless of the error.

    Acked-by: Song Liu <song@kernel.org>
    Signed-off-by: Yang Shi <shy828301@gmail.com>
    ---
    include/linux/khugepaged.h | 30 ++++++++++++------------------
    kernel/fork.c | 4 +---
    mm/huge_memory.c | 4 ++--
    mm/khugepaged.c | 18 +++++++-----------
    4 files changed, 22 insertions(+), 34 deletions(-)

    diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
    index 2fcc01891b47..0423d3619f26 100644
    --- a/include/linux/khugepaged.h
    +++ b/include/linux/khugepaged.h
    @@ -12,10 +12,10 @@ extern struct attribute_group khugepaged_attr_group;
    extern int khugepaged_init(void);
    extern void khugepaged_destroy(void);
    extern int start_stop_khugepaged(void);
    -extern int __khugepaged_enter(struct mm_struct *mm);
    +extern void __khugepaged_enter(struct mm_struct *mm);
    extern void __khugepaged_exit(struct mm_struct *mm);
    -extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    - unsigned long vm_flags);
    +extern void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    + unsigned long vm_flags);
    extern void khugepaged_min_free_kbytes_update(void);
    #ifdef CONFIG_SHMEM
    extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr);
    @@ -40,11 +40,10 @@ static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
    (transparent_hugepage_flags & \
    (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))

    -static inline int khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
    +static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
    {
    if (test_bit(MMF_VM_HUGEPAGE, &oldmm->flags))
    - return __khugepaged_enter(mm);
    - return 0;
    + __khugepaged_enter(mm);
    }

    static inline void khugepaged_exit(struct mm_struct *mm)
    @@ -53,7 +52,7 @@ static inline void khugepaged_exit(struct mm_struct *mm)
    __khugepaged_exit(mm);
    }

    -static inline int khugepaged_enter(struct vm_area_struct *vma,
    +static inline void khugepaged_enter(struct vm_area_struct *vma,
    unsigned long vm_flags)
    {
    if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
    @@ -62,27 +61,22 @@ static inline int khugepaged_enter(struct vm_area_struct *vma,
    (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
    !(vm_flags & VM_NOHUGEPAGE) &&
    !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
    - if (__khugepaged_enter(vma->vm_mm))
    - return -ENOMEM;
    - return 0;
    + __khugepaged_enter(vma->vm_mm);
    }
    #else /* CONFIG_TRANSPARENT_HUGEPAGE */
    -static inline int khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
    +static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
    {
    - return 0;
    }
    static inline void khugepaged_exit(struct mm_struct *mm)
    {
    }
    -static inline int khugepaged_enter(struct vm_area_struct *vma,
    - unsigned long vm_flags)
    +static inline void khugepaged_enter(struct vm_area_struct *vma,
    + unsigned long vm_flags)
    {
    - return 0;
    }
    -static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    - unsigned long vm_flags)
    +static inline void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    + unsigned long vm_flags)
    {
    - return 0;
    }
    static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
    unsigned long addr)
    diff --git a/kernel/fork.c b/kernel/fork.c
    index 9796897560ab..0d13baf86650 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -612,9 +612,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
    retval = ksm_fork(mm, oldmm);
    if (retval)
    goto out;
    - retval = khugepaged_fork(mm, oldmm);
    - if (retval)
    - goto out;
    + khugepaged_fork(mm, oldmm);

    prev = NULL;
    for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index 183b793fd28e..4fd5a6a79d44 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -725,8 +725,8 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
    return VM_FAULT_FALLBACK;
    if (unlikely(anon_vma_prepare(vma)))
    return VM_FAULT_OOM;
    - if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
    - return VM_FAULT_OOM;
    + khugepaged_enter(vma, vma->vm_flags);
    +
    if (!(vmf->flags & FAULT_FLAG_WRITE) &&
    !mm_forbids_zeropage(vma->vm_mm) &&
    transparent_hugepage_use_zero_page()) {
    diff --git a/mm/khugepaged.c b/mm/khugepaged.c
    index 609c1bc0a027..b69eda934d70 100644
    --- a/mm/khugepaged.c
    +++ b/mm/khugepaged.c
    @@ -365,8 +365,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
    * register it here without waiting a page fault that
    * may not happen any time soon.
    */
    - if (khugepaged_enter_vma_merge(vma, *vm_flags))
    - return -ENOMEM;
    + khugepaged_enter_vma_merge(vma, *vm_flags);
    break;
    case MADV_NOHUGEPAGE:
    *vm_flags &= ~VM_HUGEPAGE;
    @@ -475,20 +474,20 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
    return true;
    }

    -int __khugepaged_enter(struct mm_struct *mm)
    +void __khugepaged_enter(struct mm_struct *mm)
    {
    struct mm_slot *mm_slot;
    int wakeup;

    mm_slot = alloc_mm_slot();
    if (!mm_slot)
    - return -ENOMEM;
    + return;

    /* __khugepaged_exit() must not run from under us */
    VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
    if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
    free_mm_slot(mm_slot);
    - return 0;
    + return;
    }

    spin_lock(&khugepaged_mm_lock);
    @@ -504,11 +503,9 @@ int __khugepaged_enter(struct mm_struct *mm)
    mmgrab(mm);
    if (wakeup)
    wake_up_interruptible(&khugepaged_wait);
    -
    - return 0;
    }

    -int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    +void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    unsigned long vm_flags)
    {
    unsigned long hstart, hend;
    @@ -519,13 +516,12 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
    * file-private shmem THP is not supported.
    */
    if (!hugepage_vma_check(vma, vm_flags))
    - return 0;
    + return;

    hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
    hend = vma->vm_end & HPAGE_PMD_MASK;
    if (hstart < hend)
    - return khugepaged_enter(vma, vm_flags);
    - return 0;
    + khugepaged_enter(vma, vm_flags);
    }

    void __khugepaged_exit(struct mm_struct *mm)
    --
    2.26.3
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