On Sun, Oct 05, 2014 at 04:42:11PM -0700, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 3.16-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From abc40bd2eeb77eb7c2effcaf63154aad929a1d5f Mon Sep 17 00:00:00 2001
> From: Mel Gorman <mgorman@xxxxxxx>
> Date: Thu, 2 Oct 2014 19:47:42 +0100
> Subject: [PATCH] mm: numa: Do not mark PTEs pte_numa when splitting huge pages
>
> This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the
> NUMA type from the pmd to the pte"). If a huge page is being split due
> a protection change and the tail will be in a PROT_NONE vma then NUMA
> hinting PTEs are temporarily created in the protected VMA.
>
Hi Greg,
A rebased patch is below. If you would prefer to match upstream then I
suggest you pull in f8303c2582b889351e261ff18c4d8eb197a77db2 ("mm, thp:
move invariant bug check out of loop in __split_huge_page_map"). It's a
harmless patch with a small performance gain and once applied then commit
abc40bd2eeb77eb7c2effcaf63154aad929a1d5f should have no conflicts. I'm
happy with either option.
Thanks.
---8<---
>From 68798346945250e17dcddd50489a9980ffc7c7e7 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@xxxxxxx>
Date: Thu, 2 Oct 2014 19:47:42 +0100
Subject: [PATCH] mm: numa: Do not mark PTEs pte_numa when splitting huge pages
This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the
NUMA type from the pmd to the pte"). If a huge page is being split due
a protection change and the tail will be in a PROT_NONE vma then NUMA
hinting PTEs are temporarily created in the protected VMA.
VM_RW|VM_PROTNONE
|-----------------|
^
split here
In the specific case above, it should get fixed up by change_pte_range()
but there is a window of opportunity for weirdness to happen. Similarly,
if a huge page is shrunk and split during a protection update but before
pmd_numa is cleared then a pte_numa can be left behind.
Instead of adding complexity trying to deal with the case, this patch
will not mark PTEs NUMA when splitting a huge page. NUMA hinting faults
will not be triggered which is marginal in comparison to the complexity
in dealing with the corner cases during THP split.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 33514d8..03e5063 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1780,6 +1780,11 @@ static int __split_huge_page_map(struct page *page,
for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
pte_t *pte, entry;
BUG_ON(PageCompound(page+i));
+ /*
+ * Note that pmd_numa is not transferred deliberately
+ * to avoid any possibility that pte_numa leaks to
+ * a PROT_NONE VMA by accident.
+ */
entry = mk_pte(page + i, vma->vm_page_prot);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
if (!pmd_write(*pmd))
@@ -1788,8 +1793,6 @@ static int __split_huge_page_map(struct page *page,
BUG_ON(page_mapcount(page) != 1);
if (!pmd_young(*pmd))
entry = pte_mkold(entry);
- if (pmd_numa(*pmd))
- entry = pte_mknuma(entry);
pte = pte_offset_map(&_pmd, haddr);
BUG_ON(!pte_none(*pte));
set_pte_at(mm, haddr, pte, entry);
--
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