Re: [RFC PATCH 04/14] mm/migrate: Add new migrate mode MIGRATE_MT

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Fri, Feb 17, 2017 at 10:05:41AM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@nvidia.com>
> 
> This change adds a new migration mode called MIGRATE_MT to enable multi
> threaded page copy implementation inside copy_huge_page() function by
> selectively calling copy_pages_mthread() when requested. But it still
> falls back using the regular page copy mechanism instead the previous
> multi threaded attempt fails. It also attempts multi threaded copy for
> regular pages.
> 
> Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
> Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
> ---
>  include/linux/migrate_mode.h |  1 +
>  mm/migrate.c                 | 25 ++++++++++++++++++-------
>  2 files changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
> index 89c170060e5b..d344ad60f499 100644
> --- a/include/linux/migrate_mode.h
> +++ b/include/linux/migrate_mode.h
> @@ -12,6 +12,7 @@ enum migrate_mode {
>  	MIGRATE_SYNC_LIGHT	= 1<<1,
>  	MIGRATE_SYNC		= 1<<2,
>  	MIGRATE_ST		= 1<<3,
> +	MIGRATE_MT		= 1<<4,

Could you update the comment above this definition to cover the new flags.

Thanks,
Naoya Horiguchi

>  };
>  
>  #endif		/* MIGRATE_MODE_H_INCLUDED */
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 87253cb9b50a..21307219428d 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -601,6 +601,7 @@ static void copy_huge_page(struct page *dst, struct page *src,
>  {
>  	int i;
>  	int nr_pages;
> +	int rc = -EFAULT;
>  
>  	if (PageHuge(src)) {
>  		/* hugetlbfs page */
> @@ -617,10 +618,14 @@ 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_pages_mthread(dst, src, nr_pages);
> +
> +	if (rc)
> +		for (i = 0; i < nr_pages; i++) {
> +			cond_resched();
> +			copy_highpage(dst + i, src + i);
> +		}
>  }
>  
>  /*
> @@ -631,10 +636,16 @@ void migrate_page_copy(struct page *newpage, struct page *page,
>  {
>  	int cpupid;
>  
> -	if (PageHuge(page) || PageTransHuge(page))
> +	if (PageHuge(page) || PageTransHuge(page)) {
>  		copy_huge_page(newpage, page, mode);
> -	else
> -		copy_highpage(newpage, page);
> +	} else {
> +		if (mode & MIGRATE_MT) {
> +			if (copy_pages_mthread(newpage, page, 1))
> +				copy_highpage(newpage, page);
> +		} else {
> +			copy_highpage(newpage, page);
> +		}
> +	}
>  
>  	if (PageError(page))
>  		SetPageError(newpage);
> -- 
> 2.11.0
> 
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