linux-kernel - Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

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Date:   Fri, 20 Nov 2020 10:16:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>, corbet@....net,
        mike.kravetz@...cle.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        osalvador@...e.de, mhocko@...e.com, song.bao.hua@...ilicon.com
Cc:     duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct
 page size is not power of two

On 20.11.20 07:43, Muchun Song wrote:
> We only can free the unused vmemmap to the buddy system when the
> size of struct page is a power of two.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>   mm/hugetlb_vmemmap.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index c3b3fc041903..7bb749a3eea2 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -671,7 +671,8 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
>   	unsigned int order = huge_page_order(h);
>   	unsigned int vmemmap_pages;
>   
> -	if (hugetlb_free_vmemmap_disabled) {
> +	if (hugetlb_free_vmemmap_disabled ||
> +	    !is_power_of_2(sizeof(struct page))) {
>   		pr_info("disable free vmemmap pages for %s\n", h->name);
>   		return;
>   	}
> 

This patch should be merged into the original patch that introduced 
vmemmap freeing.

-- 
Thanks,

David / dhildenb