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Date: Mon, 3 Jun 2013 15:26:41 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>, Andi Kleen <andi@...stfloor.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] migrate: add migrate_entry_wait_huge()
On Tue 28-05-13 15:52:51, Naoya Horiguchi wrote:
> 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.
> 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.
>
> Note that the caller, hugetlb_fault(), gets the pointer to the "leaf"
> entry with huge_pte_offset() inside which all the arch-dependency of
> the page table structure are. So migration_entry_wait_huge() and
> __migration_entry_wait() are free from arch-dependency.
>
> ChangeLog v3:
> - use huge_pte_lockptr
>
> ChangeLog v2:
> - remove dup in migrate_entry_wait_huge()
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Reviewed-by: Rik van Riel <riel@...hat.com>
> Cc: stable@...r.kernel.org # 2.6.35
OK, this looks good to me and I guess you can safely replace
huge_pte_lockptr by &(mm)->page_table_lock so you can implement this
even without risky 1/2 of this series. The patch should be as simple as
possible especially when it goes to the stable.
Without 1/2 dependency
Reviewed-by: Michal Hocko <mhocko@...e.cz>
> ---
> include/linux/swapops.h | 3 +++
> mm/hugetlb.c | 2 +-
> mm/migrate.c | 23 ++++++++++++++++++-----
> 3 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git v3.10-rc3.orig/include/linux/swapops.h v3.10-rc3/include/linux/swapops.h
> index 47ead51..c5fd30d 100644
> --- v3.10-rc3.orig/include/linux/swapops.h
> +++ v3.10-rc3/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);
> #else
>
> #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 v3.10-rc3.orig/mm/hugetlb.c v3.10-rc3/mm/hugetlb.c
> index 8e1af32..d91a438 100644
> --- v3.10-rc3.orig/mm/hugetlb.c
> +++ v3.10-rc3/mm/hugetlb.c
> @@ -2877,7 +2877,7 @@ 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)))
> return VM_FAULT_HWPOISON_LARGE |
> diff --git v3.10-rc3.orig/mm/migrate.c v3.10-rc3/mm/migrate.c
> index 6f2df6e..64ff118 100644
> --- v3.10-rc3.orig/mm/migrate.c
> +++ v3.10-rc3/mm/migrate.c
> @@ -204,15 +204,14 @@ 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;
> @@ -240,6 +239,20 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> 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 = huge_pte_lockptr(mm, pte);
> + __migration_entry_wait(mm, pte, ptl);
> +}
> +
> #ifdef CONFIG_BLOCK
> /* Returns true if all buffers are successfully locked */
> static bool buffer_migrate_lock_buffers(struct buffer_head *head,
> --
> 1.7.11.7
>
--
Michal Hocko
SUSE Labs
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