[PATCH 79/93] mm: migration: add migrate_entry_wait_huge()

From: Luis Henriques
Date: Tue Jun 18 2013 - 07:48:32 EST -stable review patch. If anyone has any objections, please let me know.


From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

commit 30dad30922ccc733cfdbfe232090cf674dc374dc upstream.

When we have a page fault for the address which is backed by a hugepage
under migration, the kernel can't wait correctly and do busy looping on
hugepage fault until the migration finishes. As a result, users who try
to kick hugepage migration (via soft offlining, for example) occasionally
experience long delay or soft lockup.

This is because pte_offset_map_lock() can't get a correct migration entry
or a correct page table lock for hugepage. This patch introduces
migration_entry_wait_huge() to solve this.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
include/linux/swapops.h | 3 +++
mm/hugetlb.c | 2 +-
mm/migrate.c | 23 ++++++++++++++++++-----
3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 47ead51..c5fd30d 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -137,6 +137,7 @@ static inline void make_migration_entry_read(swp_entry_t *entry)

extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
unsigned long address);
+extern void migration_entry_wait_huge(struct mm_struct *mm, pte_t *pte);

#define make_migration_entry(page, write) swp_entry(0, 0)
@@ -148,6 +149,8 @@ static inline int is_migration_entry(swp_entry_t swp)
static inline void make_migration_entry_read(swp_entry_t *entryp) { }
static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
unsigned long address) { }
+static inline void migration_entry_wait_huge(struct mm_struct *mm,
+ pte_t *pte) { }
static inline int is_write_migration_entry(swp_entry_t entry)
return 0;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 74b8327..c6557ef 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2769,7 +2769,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
if (ptep) {
entry = huge_ptep_get(ptep);
if (unlikely(is_hugetlb_entry_migration(entry))) {
- migration_entry_wait(mm, (pmd_t *)ptep, address);
+ migration_entry_wait_huge(mm, ptep);
return 0;
} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
diff --git a/mm/migrate.c b/mm/migrate.c
index 65cc229..41e906a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -182,15 +182,14 @@ static void remove_migration_ptes(struct page *old, struct page *new)
* get to the page and wait until migration is finished.
* When we return from this function the fault will be retried.
-void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
- unsigned long address)
+static void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
+ spinlock_t *ptl)
- pte_t *ptep, pte;
- spinlock_t *ptl;
+ pte_t pte;
swp_entry_t entry;
struct page *page;

- ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+ spin_lock(ptl);
pte = *ptep;
if (!is_swap_pte(pte))
goto out;
@@ -218,6 +217,20 @@ out:
pte_unmap_unlock(ptep, ptl);

+void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
+ unsigned long address)
+ spinlock_t *ptl = pte_lockptr(mm, pmd);
+ pte_t *ptep = pte_offset_map(pmd, address);
+ __migration_entry_wait(mm, ptep, ptl);
+void migration_entry_wait_huge(struct mm_struct *mm, pte_t *pte)
+ spinlock_t *ptl = &(mm)->page_table_lock;
+ __migration_entry_wait(mm, pte, ptl);
/* Returns true if all buffers are successfully locked */
static bool buffer_migrate_lock_buffers(struct buffer_head *head,

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/