linux-kernel - Re: [PATCH 3/4] mm/hugetlb: make hugetlb migration callback CMA aware

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Date:   Wed, 15 Jul 2020 11:51:14 +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>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 3/4] mm/hugetlb: make hugetlb migration callback CMA aware

On 7/15/20 7:05 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....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@...cle.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

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