linux-kernel - Re: [PATCH v2] mm: hugetlb: optionally allocate gigantic hugepages using cma

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Message-ID: <20200310090121.GB8447@dhcp22.suse.cz>
Date:   Tue, 10 Mar 2020 10:01:21 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        Rik van Riel <riel@...riel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH v2] mm: hugetlb: optionally allocate gigantic hugepages
 using cma

On Mon 09-03-20 17:25:24, Roman Gushchin wrote:
[...]
> 2) Run-time allocations of gigantic hugepages are performed using the
>    cma allocator and the dedicated cma area

[...]
> @@ -1237,6 +1246,23 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
>  {
>  	unsigned long nr_pages = 1UL << huge_page_order(h);
>  
> +	if (IS_ENABLED(CONFIG_CMA) && hugetlb_cma[0]) {
> +		struct page *page;
> +		int nid;
> +
> +		for_each_node_mask(nid, *nodemask) {
> +			if (!hugetlb_cma[nid])
> +				break;
> +
> +			page = cma_alloc(hugetlb_cma[nid], nr_pages,
> +					 huge_page_order(h), true);
> +			if (page)
> +				return page;
> +		}
> +
> +		return NULL;

Is there any strong reason why the alloaction annot fallback to non-CMA
allocator when the cma is depleted?

> +	}
> +
>  	return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
>  }

-- 
Michal Hocko
SUSE Labs