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Subject: Re: [PATCH 3/4] mm/hugetlb: make hugetlb migration callback CMA aware
To:     js1304@gmail.com, Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        kernel-team@lge.com, 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>
References: <1594789529-6206-1-git-send-email-iamjoonsoo.kim@lge.com>
 <1594789529-6206-3-git-send-email-iamjoonsoo.kim@lge.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <d2a26d81-ce9a-c24c-a2f7-d3b1fa2184d4@suse.cz>
Date:   Wed, 15 Jul 2020 11:51:14 +0200
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On 7/15/20 7:05 AM, js1304@gmail.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> new_non_cma_page() in gup.c requires to allocate the new page that is not
> on the CMA area. new_non_cma_page() implements it by using allocation
> scope APIs.
> 
> However, there is a work-around for hugetlb. Normal hugetlb page
> allocation API for migration is alloc_huge_page_nodemask(). It consists
> of two steps. First is dequeing from the pool. Second is, if there is no
> available page on the queue, allocating by using the page allocator.
> 
> new_non_cma_page() can't use this API since first step (deque) isn't
> aware of scope API to exclude CMA area. So, new_non_cma_page() exports
> hugetlb internal function for the second step, alloc_migrate_huge_page(),
> to global scope and uses it directly. This is suboptimal since hugetlb
> pages on the queue cannot be utilized.
> 
> This patch tries to fix this situation by making the deque function on
> hugetlb CMA aware. In the deque function, CMA memory is skipped if
> PF_MEMALLOC_NOCMA flag is found.
> 
> Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

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