linux-kernel - Re: [PATCH 1/1] mm/migrate: do not call prep_transhuge_page if !thp_migration

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Date:   Mon, 20 Nov 2017 11:33:06 -0500
From:   "Zi Yan" <zi.yan@...rutgers.edu>
To:     "Andrea Reale" <ar@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, n-horiguchi@...jp.nec.com,
        akpm@...ux-foundation.org, jglisse@...hat.com, realean2@...ibm.com
Subject: Re: [PATCH 1/1] mm/migrate: do not call prep_transhuge_page if
 !thp_migration_supported

Hi Andrea,

Thanks for pointing this out.

I think the problem is that we should not prep_transhuge_page(new_page)
unless new_page is allocated and PageTransHuge(). And several lines above,
the allocation flags and the order is changed to make new_page a THP
only if thp_migration_supported() is true.

Does the patch below look better?

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 895ec0c..725eac5 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -54,7 +54,7 @@ static inline struct page *new_page_nodemask(struct page *page,
 	new_page = __alloc_pages_nodemask(gfp_mask, order,
 				preferred_nid, nodemask);

-	if (new_page && PageTransHuge(page))
+	if (new_page && PageTransHuge(new_page))
 		prep_transhuge_page(new_page);

 	return new_page;
-- 


--
Best Regards
Yan Zi

On 20 Nov 2017, at 11:17, Andrea Reale wrote:

> new_page_nodemask in linux/migrate.h should not call prep_transhuge_page
> if thp_migration_support is false.
>
> Fixes commit 8135d8926c08 ("mm: memory_hotplug: memory hotremove supports
> thp migration")
>
> Signed-off-by: Andrea Reale <ar@...ux.vnet.ibm.com>
> ---
>  include/linux/migrate.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 895ec0c..725eac5 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -54,7 +54,7 @@ static inline struct page *new_page_nodemask(struct page *page,
>  	new_page = __alloc_pages_nodemask(gfp_mask, order,
>  				preferred_nid, nodemask);
>
> -	if (new_page && PageTransHuge(page))
> +	if (thp_migration_supported() && new_page && PageTransHuge(page))
>  		prep_transhuge_page(new_page);
>
>  	return new_page;
> -- 
> 2.7.4

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