RE: [PATCH 1/4] mm/page_alloc: fix non cma alloc context

From: David Laight <David.Laight@ACULAB.COM>
To: "'js1304@gmail.com'" <js1304@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-team@lge.com" <kernel-team@lge.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Christoph Hellwig <hch@infradead.org>,
	Roman Gushchin <guro@fb.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	"Naoya Horiguchi" <n-horiguchi@ah.jp.nec.com>,
	Michal Hocko <mhocko@suse.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH 1/4] mm/page_alloc: fix non cma alloc context
Date: Fri, 17 Jul 2020 08:32:07 +0000	[thread overview]
Message-ID: <be55deff4ef1453983522d247bd36110@AcuMS.aculab.com> (raw)
In-Reply-To: <1594789529-6206-1-git-send-email-iamjoonsoo.kim@lge.com>

From: js1304@gmail.com
> Sent: 15 July 2020 06:05
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> Currently, preventing cma area in page allocation is implemented by using
> current_gfp_context(). However, there are two problems of this
> implementation.
...
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6416d08..cd53894 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
...
> @@ -3693,6 +3691,16 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
>  	return alloc_flags;
>  }
> 
> +static inline void current_alloc_flags(gfp_t gfp_mask,
> +				unsigned int *alloc_flags)
> +{
> +	unsigned int pflags = READ_ONCE(current->flags);
> +
> +	if (!(pflags & PF_MEMALLOC_NOCMA) &&
> +		gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> +		*alloc_flags |= ALLOC_CMA;
> +}
> +

I'd guess this would be easier to understand and probably generate
better code if renamed and used as:
	alloc_flags |= can_alloc_cma(gpf_mask);

Given it is a 'static inline' the compiler might end up
generating the same code.
If you needed to clear a flag doing:
	alloc_flags = current_alloc_flags(gpf_mask, alloc_flags);
is much better for non-inlined function.

	David

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