linux-kernel - Re: [PATCH v4 07/11] mm/gup: use a standard migration target allocation callback

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Date:   Tue, 7 Jul 2020 13:46:14 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     js1304@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 07/11] mm/gup: use a standard migration target
 allocation callback

On Tue 07-07-20 16:44:45, Joonsoo Kim wrote:
[...]
> @@ -1551,9 +1552,12 @@ struct page *alloc_migration_target(struct page *page, unsigned long private)
>  
>  		gfp_mask |= htlb_alloc_mask(h);
>  		return alloc_huge_page_nodemask(h, nid, mtc->nmask,
> -						gfp_mask, false);
> +						gfp_mask, mtc->skip_cma);
>  	}
>  
> +	if (mtc->skip_cma)
> +		flags = memalloc_nocma_save();
> +

As already mentioned in previous email this is a completely wrong usage
of the scope API. The scope should be defined by the caller and this
should be all transparent by the allocator layer.

>  	if (PageTransHuge(page)) {
>  		/*
>  		 * clear __GFP_RECALIM since GFP_TRANSHUGE is the gfp_mask
> @@ -1572,6 +1576,9 @@ struct page *alloc_migration_target(struct page *page, unsigned long private)
>  	if (new_page && PageTransHuge(new_page))
>  		prep_transhuge_page(new_page);
>  
> +	if (mtc->skip_cma)
> +		memalloc_nocma_restore(flags);
> +
>  	return new_page;
>  }
>  
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs