Patchwork powerpc/mm: Make sure a local_irq_disable prevent a parallel THP split

login
register
mail settings
Submitter Aneesh Kumar K.V
Date March 15, 2014, 10:47 a.m.
Message ID <1394880478-770-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/330643/
State Accepted
Commit 346519a1606e196bd5f11b9f5eacaf60f70477a1
Headers show

Comments

Aneesh Kumar K.V - March 15, 2014, 10:47 a.m.
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

We have generic code like the one in get_futex_key that assume that
a local_irq_disable prevents a parallel THP split. Support that by
adding a dummy smp call function after setting _PAGE_SPLITTING. Code
paths like get_user_pages_fast still need to check for _PAGE_SPLITTING
after disabling IRQ which indicate that a parallel THP splitting is
ongoing. Now if they don't find _PAGE_SPLITTING set, then we can be
sure that parallel split will now block in pmdp_splitting flush
until we enables IRQ

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/mm/pgtable_64.c | 5 +++++
 1 file changed, 5 insertions(+)
Rik van Riel - March 15, 2014, 7:25 p.m.
On 03/15/2014 06:47 AM, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> We have generic code like the one in get_futex_key that assume that
> a local_irq_disable prevents a parallel THP split. Support that by
> adding a dummy smp call function after setting _PAGE_SPLITTING. Code
> paths like get_user_pages_fast still need to check for _PAGE_SPLITTING
> after disabling IRQ which indicate that a parallel THP splitting is
> ongoing. Now if they don't find _PAGE_SPLITTING set, then we can be
> sure that parallel split will now block in pmdp_splitting flush
> until we enables IRQ
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

Acked-by: Rik van Riel <riel@redhat.com>

Patch

diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index 62bf5e8e78da..f6ce1f111f5b 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -647,6 +647,11 @@  void pmdp_splitting_flush(struct vm_area_struct *vma,
 		if (old & _PAGE_HASHPTE)
 			hpte_do_hugepage_flush(vma->vm_mm, address, pmdp);
 	}
+	/*
+	 * This ensures that generic code that rely on IRQ disabling
+	 * to prevent a parallel THP split work as expected.
+	 */
+	kick_all_cpus_sync();
 }
 
 /*