Re: [PATCH 1/9] migrate: add migrate_entry_wait_huge()

[Simon Jeons <simon.jeons@gmail.com>]

Hi Naoya,
On 02/22/2013 03:41 AM, 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 until the migration
> finishes. This is because pte_offset_map_lock() can't get a correct

It seems that current hugetlb_fault still wait hugetlb page under 
migration, how can it work without lock 2MB memory?

> migration entry for hugepage. This patch adds migration_entry_wait_huge()
> to separate code path between normal pages and hugepages.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
>   include/linux/hugetlb.h |  2 ++
>   include/linux/swapops.h |  4 ++++
>   mm/hugetlb.c            |  4 ++--
>   mm/migrate.c            | 24 ++++++++++++++++++++++++
>   4 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git v3.8.orig/include/linux/hugetlb.h v3.8/include/linux/hugetlb.h
> index 0c80d3f..40b27f6 100644
> --- v3.8.orig/include/linux/hugetlb.h
> +++ v3.8/include/linux/hugetlb.h
> @@ -43,6 +43,7 @@ int hugetlb_mempolicy_sysctl_handler(struct ctl_table *, int,
>   #endif
>   
>   int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *, struct vm_area_struct *);
> +int is_hugetlb_entry_migration(pte_t pte);
>   int follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *,
>   			struct page **, struct vm_area_struct **,
>   			unsigned long *, int *, int, unsigned int flags);
> @@ -109,6 +110,7 @@ static inline unsigned long hugetlb_total_pages(void)
>   #define follow_hugetlb_page(m,v,p,vs,a,b,i,w)	({ BUG(); 0; })
>   #define follow_huge_addr(mm, addr, write)	ERR_PTR(-EINVAL)
>   #define copy_hugetlb_page_range(src, dst, vma)	({ BUG(); 0; })
> +#define is_hugetlb_entry_migration(pte)		({ BUG(); 0; })
>   #define hugetlb_prefault(mapping, vma)		({ BUG(); 0; })
>   static inline void hugetlb_report_meminfo(struct seq_file *m)
>   {
> diff --git v3.8.orig/include/linux/swapops.h v3.8/include/linux/swapops.h
> index 47ead51..f68efdd 100644
> --- v3.8.orig/include/linux/swapops.h
> +++ v3.8/include/linux/swapops.h
> @@ -137,6 +137,8 @@ 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, pmd_t *pmd,
> +					unsigned long address);
>   #else
>   
>   #define make_migration_entry(page, write) swp_entry(0, 0)
> @@ -148,6 +150,8 @@ 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, pmd_t *pmd,
> +					 unsigned long address) { }
>   static inline int is_write_migration_entry(swp_entry_t entry)
>   {
>   	return 0;
> diff --git v3.8.orig/mm/hugetlb.c v3.8/mm/hugetlb.c
> index 546db81..351025e 100644
> --- v3.8.orig/mm/hugetlb.c
> +++ v3.8/mm/hugetlb.c
> @@ -2313,7 +2313,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
>   	return -ENOMEM;
>   }
>   
> -static int is_hugetlb_entry_migration(pte_t pte)
> +int is_hugetlb_entry_migration(pte_t pte)
>   {
>   	swp_entry_t swp;
>   
> @@ -2823,7 +2823,7 @@ 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, (pmd_t *)ptep, address);
>   			return 0;
>   		} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
>   			return VM_FAULT_HWPOISON_LARGE |
> diff --git v3.8.orig/mm/migrate.c v3.8/mm/migrate.c
> index 2fd8b4a..7d84f4c 100644
> --- v3.8.orig/mm/migrate.c
> +++ v3.8/mm/migrate.c
> @@ -236,6 +236,30 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>   	pte_unmap_unlock(ptep, ptl);
>   }
>   
> +void migration_entry_wait_huge(struct mm_struct *mm, pmd_t *pmd,
> +				unsigned long address)
> +{
> +	spinlock_t *ptl = pte_lockptr(mm, pmd);
> +	pte_t pte;
> +	swp_entry_t entry;
> +	struct page *page;
> +
> +	spin_lock(ptl);
> +	pte = huge_ptep_get((pte_t *)pmd);
> +	if (!is_hugetlb_entry_migration(pte))
> +		goto out;
> +	entry = pte_to_swp_entry(pte);
> +	page = migration_entry_to_page(entry);
> +	if (!get_page_unless_zero(page))
> +		goto out;
> +	spin_unlock(ptl);
> +	wait_on_page_locked(page);
> +	put_page(page);
> +	return;
> +out:
> +	spin_unlock(ptl);
> +}
> +
>   #ifdef CONFIG_BLOCK
>   /* Returns true if all buffers are successfully locked */
>   static bool buffer_migrate_lock_buffers(struct buffer_head *head,

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