The patch titled
Subject: mm/mprotect.c: don't touch single threaded PTEs which are on the right node
has been added to the -mm tree. Its filename is
dont-touch-single-threaded-ptes-which-are-on-the-right-node.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dont-touch-single-threaded-ptes-which-are-on-the-right-node.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dont-touch-single-threaded-ptes-which-are-on-the-right-node.patch
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------------------------------------------------------
From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Subject: mm/mprotect.c: don't touch single threaded PTEs which are on the right node
We had some problems with pages getting unmapped in single threaded
affinitized processes. It was tracked down to NUMA scanning.
In this case it doesn't make any sense to unmap pages if the process is
single threaded and the page is already on the node the process is running
on.
Add a check for this case into the numa protection code, and skip
unmapping if true.
In theory the process could be migrated later, but we will eventually
rescan and unmap and migrate then.
In theory this could be made more fancy: remembering this state per
process or even whole mm. However that would need extra tracking and be
more complicated, and the simple check seems to work fine so far.
Link: http://lkml.kernel.org/r/1476288949-20970-1-git-send-email-andi@xxxxxxxxxxxxxx
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mprotect.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff -puN mm/mprotect.c~dont-touch-single-threaded-ptes-which-are-on-the-right-node mm/mprotect.c
--- a/mm/mprotect.c~dont-touch-single-threaded-ptes-which-are-on-the-right-node
+++ a/mm/mprotect.c
@@ -70,11 +70,17 @@ static unsigned long change_pte_range(st
pte_t *pte, oldpte;
spinlock_t *ptl;
unsigned long pages = 0;
+ int target_node = -1;
pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
if (!pte)
return 0;
+ if (prot_numa &&
+ !(vma->vm_flags & VM_SHARED) &&
+ atomic_read(&vma->vm_mm->mm_users) == 1)
+ target_node = cpu_to_node(raw_smp_processor_id());
+
arch_enter_lazy_mmu_mode();
do {
oldpte = *pte;
@@ -96,6 +102,13 @@ static unsigned long change_pte_range(st
/* Avoid TLB flush if possible */
if (pte_protnone(oldpte))
continue;
+
+ /*
+ * Don't mess with PTEs if page is already on the node
+ * a single-threaded process is running on.
+ */
+ if (target_node == page_to_nid(page))
+ continue;
}
ptent = ptep_modify_prot_start(mm, addr, pte);
_
Patches currently in -mm which might be from ak@xxxxxxxxxxxxxxx are
dont-touch-single-threaded-ptes-which-are-on-the-right-node.patch
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