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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Message-ID: <20201120082552.GI3200@dhcp22.suse.cz>
Date:   Fri, 20 Nov 2020 09:25:52 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     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, song.bao.hua@...ilicon.com,
        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 Fri 20-11-20 14:43:25, 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.

Can we actually have !power_of_2 struct pages?

> 
> 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;
>  	}
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs