linux-kernel - Re: [PATCH v3 6/8] mm/gup: use a standard migration target allocation callback

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Message-ID: <1693d7a8-4384-8fd8-69a2-55552329a34d@suse.cz>
Date:   Fri, 3 Jul 2020 17:56:29 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 6/8] mm/gup: use a standard migration target allocation
 callback

On 6/23/20 8:13 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> There is a well-defined migration target allocation callback.
> It's mostly similar with new_non_cma_page() except considering CMA pages.
> 
> This patch adds a CMA consideration to the standard migration target
> allocation callback and use it on gup.c.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

But a suggestion below.

> ---
>  mm/gup.c      | 57 ++++++++-------------------------------------------------
>  mm/internal.h |  1 +
>  mm/migrate.c  |  4 +++-
>  3 files changed, 12 insertions(+), 50 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 15be281..f6124e3 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1608,56 +1608,15 @@ static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>  }
>  
>  #ifdef CONFIG_CMA
> -static struct page *new_non_cma_page(struct page *page, unsigned long private)
> +static struct page *alloc_migration_target_non_cma(struct page *page, unsigned long private)
>  {

...

> +	struct migration_target_control mtc = {
> +		.nid = page_to_nid(page),
> +		.gfp_mask = GFP_USER | __GFP_NOWARN,
> +		.skip_cma = true,
> +	};
>  
> -	return __alloc_pages_node(nid, gfp_mask, 0);
> +	return alloc_migration_target(page, (unsigned long)&mtc);

Do we really need this wrapper? The only user is check_and_migrate_cma_pages so
just opencode it?