On Sat, Oct 04, 2014 at 07:48:04PM -0700, David Rientjes wrote: > 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_advise(), > 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_advise() 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. > > Cc: <[email protected]> > Reported-by: Suleiman Souhlal <[email protected]> > Signed-off-by: David Rientjes <[email protected]>
Okay, I've looked once again and it seems your approach is better. Although, I don't like that we need to pass down vma->vm_flags to every khugepaged_enter() and khugepaged_enter_vma_merge(). My proposal is below. Build-tested only. And I don't think this is subject for stable@: no crash or serious misbehaviour. Registering to khugepaged is postponed until first page fault. Not a big deal. >From 6434d87a313317bcbc98313794840c366ba39ba1 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <[email protected]> Date: Mon, 6 Oct 2014 17:52:17 +0300 Subject: [PATCH] thp: fix registering VMA into khugepaged on madvise(MADV_HUGEPAGE) hugepage_madvise() tries to register VMA into khugepaged with khugepaged_enter_vma_merge() on madvise(MADV_HUGEPAGE). Unfortunately it's effectevely nop, since khugepaged_enter_vma_merge() rely on vma->vm_flags which has not yet updated by the time of hugepage_madvise(). Let's create a variant of khugepaged_enter_vma_merge() which takes external vm_flags to consider. At the moment there's only two users for such function: hugepage_madvise() and vma_merge(). Reported-by: Suleiman Souhlal <[email protected]> Signed-off-by: Kirill A. Shutemov <[email protected]> --- include/linux/khugepaged.h | 9 +++++++++ mm/huge_memory.c | 27 ++++++++++++++++++++------- mm/mmap.c | 6 +++--- 3 files changed, 32 insertions(+), 10 deletions(-) diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h index 6b394f0b5148..bb25e323ee2d 100644 --- a/include/linux/khugepaged.h +++ b/include/linux/khugepaged.h @@ -7,6 +7,8 @@ extern int __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); +extern int __khugepaged_enter_vma_merge(struct vm_area_struct *vma, + vm_flags_t vm_flags); #define khugepaged_enabled() \ (transparent_hugepage_flags & \ @@ -62,6 +64,13 @@ static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma) { return 0; } + +static inline int __khugepaged_enter_vma_merge(struct vm_area_struct *vma, + vm_flags_t vm_flags) +{ + return 0; +} + #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ #endif /* _LINUX_KHUGEPAGED_H */ diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 017aff657ef5..4b0afc076827 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1944,7 +1944,7 @@ out: #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE) int hugepage_madvise(struct vm_area_struct *vma, - unsigned long *vm_flags, int advice) + vm_flags_t *vm_flags, int advice) { switch (advice) { case MADV_HUGEPAGE: @@ -1969,8 +1969,7 @@ int hugepage_madvise(struct vm_area_struct *vma, * register it here without waiting a page fault that * may not happen any time soon. */ - if (unlikely(khugepaged_enter_vma_merge(vma))) - return -ENOMEM; + return __khugepaged_enter_vma_merge(vma, *vm_flags); break; case MADV_NOHUGEPAGE: /* @@ -2070,7 +2069,8 @@ int __khugepaged_enter(struct mm_struct *mm) return 0; } -int khugepaged_enter_vma_merge(struct vm_area_struct *vma) +int __khugepaged_enter_vma_merge(struct vm_area_struct *vma, + vm_flags_t vm_flags) { unsigned long hstart, hend; if (!vma->anon_vma) @@ -2082,14 +2082,27 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma) if (vma->vm_ops) /* khugepaged not yet working on file or special mappings */ return 0; - VM_BUG_ON(vma->vm_flags & VM_NO_THP); + VM_BUG_ON(vm_flags & VM_NO_THP); hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; hend = vma->vm_end & HPAGE_PMD_MASK; - if (hstart < hend) - return khugepaged_enter(vma); + if (hstart >= hend) + return 0; + if (test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags)) + return 0; + if (vm_flags & VM_NOHUGEPAGE) + return 0; + if (khugepaged_always()) + return __khugepaged_enter(vma->vm_mm); + if (khugepaged_req_madv() && vm_flags & VM_HUGEPAGE) + return __khugepaged_enter(vma->vm_mm); return 0; } +int khugepaged_enter_vma_merge(struct vm_area_struct *vma) +{ + return __khugepaged_enter_vma_merge(vma, vma->vm_flags); +} + void __khugepaged_exit(struct mm_struct *mm) { struct mm_slot *mm_slot; diff --git a/mm/mmap.c b/mm/mmap.c index c0a3637cdb64..19fee85f0b12 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1009,8 +1009,8 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, */ struct vm_area_struct *vma_merge(struct mm_struct *mm, struct vm_area_struct *prev, unsigned long addr, - unsigned long end, unsigned long vm_flags, - struct anon_vma *anon_vma, struct file *file, + unsigned long end, vm_flags_t vm_flags, + struct anon_vma *anon_vma, struct file *file, pgoff_t pgoff, struct mempolicy *policy) { pgoff_t pglen = (end - addr) >> PAGE_SHIFT; @@ -1056,7 +1056,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm, end, prev->vm_pgoff, NULL); if (err) return NULL; - khugepaged_enter_vma_merge(prev); + __khugepaged_enter_vma_merge(prev, vm_flags); return prev; } -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
