Re: [PATCH 4/5] mm: migrate: Add copy_page_mt into migrate_pages.

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

On 11/22/2016 09:55 PM, Zi Yan wrote:
> From: Zi Yan <zi.yan@cs.rutgers.edu>
> 
> From: Zi Yan <ziy@nvidia.com>
> 
> An option is added to move_pages() syscall to use multi-threaded
> page migration.
> 


> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
> ---
>  include/linux/migrate_mode.h   |  1 +
>  include/uapi/linux/mempolicy.h |  2 ++
>  mm/migrate.c                   | 27 +++++++++++++++++++--------
>  3 files changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
> index 0e2deb8..c711e2a 100644
> --- a/include/linux/migrate_mode.h
> +++ b/include/linux/migrate_mode.h
> @@ -11,6 +11,7 @@ enum migrate_mode {
>  	MIGRATE_ASYNC		= 1<<0,
>  	MIGRATE_SYNC_LIGHT	= 1<<1,
>  	MIGRATE_SYNC		= 1<<2,
> +	MIGRATE_MT			= 1<<3,

MIGRATE_MTHREAD should be better.

>  };
> 
>  #endif		/* MIGRATE_MODE_H_INCLUDED */
> diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h
> index 9cd8b21..5d42dc6 100644
> --- a/include/uapi/linux/mempolicy.h
> +++ b/include/uapi/linux/mempolicy.h
> @@ -54,6 +54,8 @@ enum mpol_rebind_step {
>  #define MPOL_MF_LAZY	 (1<<3)	/* Modifies '_MOVE:  lazy migrate on fault */
>  #define MPOL_MF_INTERNAL (1<<4)	/* Internal flags start here */
> 
> +#define MPOL_MF_MOVE_MT  (1<<6)	/* Use multi-threaded page copy routine */
> +

s/MPOL_MF_MOVE_MT/MPOL_MF_MOVE_MTHREAD/

>  #define MPOL_MF_VALID	(MPOL_MF_STRICT   | 	\
>  			 MPOL_MF_MOVE     | 	\
>  			 MPOL_MF_MOVE_ALL)
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4a4cf48..244ece6 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -634,6 +634,7 @@ static void copy_huge_page(struct page *dst, struct page *src,
>  {
>  	int i;
>  	int nr_pages;
> +	int rc = -EFAULT;
> 
>  	if (PageHuge(src)) {
>  		/* hugetlbfs page */
> @@ -650,10 +651,14 @@ static void copy_huge_page(struct page *dst, struct page *src,
>  		nr_pages = hpage_nr_pages(src);
>  	}
> 
> -	for (i = 0; i < nr_pages; i++) {
> -		cond_resched();
> -		copy_highpage(dst + i, src + i);
> -	}
> +	if (mode & MIGRATE_MT)
> +		rc = copy_page_mt(dst, src, nr_pages);
> +
> +	if (rc)
> +		for (i = 0; i < nr_pages; i++) {
> +			cond_resched();
> +			copy_highpage(dst + i, src + i);
> +		}
>  }

So this is the case where MIGRATE_MT is mentioned or when it fails.
A small documentation above the code block should be good.

> 
>  /*
> @@ -1461,11 +1466,16 @@ static struct page *new_page_node(struct page *p, unsigned long private,
>   */
>  static int do_move_page_to_node_array(struct mm_struct *mm,
>  				      struct page_to_node *pm,
> -				      int migrate_all)
> +				      int migrate_all,
> +					  int migrate_use_mt)
>  {
>  	int err;
>  	struct page_to_node *pp;
>  	LIST_HEAD(pagelist);
> +	enum migrate_mode mode = MIGRATE_SYNC;
> +
> +	if (migrate_use_mt)
> +		mode |= MIGRATE_MT;
> 
>  	down_read(&mm->mmap_sem);
> 
> @@ -1542,7 +1552,7 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
>  	err = 0;
>  	if (!list_empty(&pagelist)) {
>  		err = migrate_pages(&pagelist, new_page_node, NULL,
> -				(unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
> +				(unsigned long)pm, mode, MR_SYSCALL);
>  		if (err)
>  			putback_movable_pages(&pagelist);
>  	}
> @@ -1619,7 +1629,8 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> 
>  		/* Migrate this chunk */
>  		err = do_move_page_to_node_array(mm, pm,
> -						 flags & MPOL_MF_MOVE_ALL);
> +						 flags & MPOL_MF_MOVE_ALL,
> +						 flags & MPOL_MF_MOVE_MT);
>  		if (err < 0)
>  			goto out_pm;
> 
> @@ -1726,7 +1737,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
>  	nodemask_t task_nodes;
> 
>  	/* Check flags */
> -	if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
> +	if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL|MPOL_MF_MOVE_MT))
>  		return -EINVAL;

Wondering if do_move_pages_to_node_array() is the only place which
needs to be changed to accommodate this.

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