On Thu, Mar 03, 2016 at 01:50:58PM +0300, Kirill A. Shutemov wrote:

On Thu, Mar 03, 2016 at 04:41:52PM +0900, Naoya Horiguchi wrote:

quoted

If one of callers of page migration starts to handle thp, memory management code
start to see pmd migration entry, so we need to prepare for it before enabling.
This patch changes various code point which checks the status of given pmds in
order to prevent race between thp migration and the pmd-related works.

Signed-off-by: Naoya Horiguchi <redacted>
---
 arch/x86/mm/gup.c  |  3 +++
 fs/proc/task_mmu.c | 25 +++++++++++++--------
 mm/gup.c           |  8 +++++++
 mm/huge_memory.c   | 66 ++++++++++++++++++++++++++++++++++++++++++++++++------
 mm/memcontrol.c    |  2 ++
 mm/memory.c        |  5 +++++
 6 files changed, 93 insertions(+), 16 deletions(-)

diff --git v4.5-rc5-mmotm-2016-02-24-16-18/arch/x86/mm/gup.c v4.5-rc5-mmotm-2016-02-24-16-18_patched/arch/x86/mm/gup.c
index f8d0b5e..34c3d43 100644
--- v4.5-rc5-mmotm-2016-02-24-16-18/arch/x86/mm/gup.c
+++ v4.5-rc5-mmotm-2016-02-24-16-18_patched/arch/x86/mm/gup.c

@@ -10,6 +10,7 @@
 #include <linux/highmem.h>
 #include <linux/swap.h>
 #include <linux/memremap.h>
+#include <linux/swapops.h>

 #include <asm/pgtable.h>

@@ -210,6 +211,8 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 		if (pmd_none(pmd))
 			return 0;
 		if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
+			if (unlikely(is_pmd_migration_entry(pmd)))
+				return 0;

Hm. I've expected to see bunch of pmd_none() to pmd_present() conversions.
That's seems a right way guard the code. Otherwise we wound need even more
checks once PMD-level swap is implemented.

Yes, I agree. I'll try some for this pmd_none/pmd_present issue.

Thanks,
Naoya

I think we need to check for migration entires only if we have something
to do with migration. In all other cases pmd_present() should be enough to
bail out.

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