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: <stable@xxxxxxxxxxxxxxx> > Reported-by: Suleiman Souhlal <suleiman@xxxxxxxxxx> > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> Look like rather complex fix for a not that complex bug. What about untested patch below? From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Sun, 5 Oct 2014 21:22:43 +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 move khugepaged_enter_vma_merge() to the end of madvise_behavior(). Now we also have chance to catch VMAs which become good for THP after vma_merge(). Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> --- mm/huge_memory.c | 8 +++----- mm/madvise.c | 6 ++++++ 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f8ffd9412ec5..f84d52158a66 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1966,12 +1966,10 @@ int hugepage_madvise(struct vm_area_struct *vma, *vm_flags &= ~VM_NOHUGEPAGE; *vm_flags |= VM_HUGEPAGE; /* - * If the vma become good for khugepaged to scan, - * register it here without waiting a page fault that - * may not happen any time soon. + * vma->vm_flags is not yet updated here. madvise_behavior() + * will take care to register it in khugepaged once flags + * updated. */ - if (unlikely(khugepaged_enter_vma_merge(vma))) - return -ENOMEM; break; case MADV_NOHUGEPAGE: /* diff --git a/mm/madvise.c b/mm/madvise.c index 0938b30da4ab..60effd2c5e9c 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -128,6 +128,12 @@ success: */ vma->vm_flags = new_flags; + /* + * If the vma become good for khugepaged to scan, register it here + * without waiting a page fault that may not happen any time soon. + */ + if (unlikely(khugepaged_enter_vma_merge(vma))) + error = -ENOMEM; out: if (error == -ENOMEM) error = -EAGAIN; -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html