From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Suleiman Souhlal <suleiman@google.com>,
stable@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [patch for-3.17] mm, thp: fix collapsing of hugepages on madvise
Date: Sun, 5 Oct 2014 21:41:15 +0300 [thread overview]
Message-ID: <20141005184115.GA21713@node.dhcp.inet.fi> (raw)
In-Reply-To: <alpine.DEB.2.02.1410041947080.7055@chino.kir.corp.google.com>
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@vger.kernel.org>
> Reported-by: Suleiman Souhlal <suleiman@google.com>
> Signed-off-by: David Rientjes <rientjes@google.com>
Look like rather complex fix for a not that complex bug.
What about untested patch below?
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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@linux.intel.com>
---
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
next prev parent reply other threads:[~2014-10-05 18:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-05 2:48 [patch for-3.17] mm, thp: fix collapsing of hugepages on madvise David Rientjes
2014-10-05 17:15 ` Linus Torvalds
2014-10-05 18:41 ` Kirill A. Shutemov [this message]
2014-10-05 18:51 ` Linus Torvalds
2014-10-06 9:42 ` David Rientjes
2014-10-06 15:03 ` Kirill A. Shutemov
2014-10-06 20:53 ` David Rientjes
2014-10-15 21:13 ` [patch resend] " David Rientjes
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