linux-kernel - Re: [PATCH v8 10/12] mm/hugetlb: Introduce nr_free_vmemmap

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Message-ID: <20201210101526.GA4525@localhost.localdomain>
Date:   Thu, 10 Dec 2020 11:15:26 +0100
From:   Oscar Salvador <osalvador@...e.de>
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,
        mhocko@...e.com, song.bao.hua@...ilicon.com, david@...hat.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 v8 10/12] mm/hugetlb: Introduce nr_free_vmemmap_pages in
 the struct hstate

On Thu, Dec 10, 2020 at 11:55:24AM +0800, Muchun Song wrote:
> +void __init hugetlb_vmemmap_init(struct hstate *h)
> +{
> +	unsigned int nr_pages = pages_per_huge_page(h);
> +	unsigned int vmemmap_pages;
> +
> +	/* We cannot optimize if a "struct page" crosses page boundaries. */
> +	if (!is_power_of_2(sizeof(struct page)))
> +		return;
> +
> +	if (!hugetlb_free_vmemmap_enabled)
> +		return;

I think it would make sense to squash the last patch and this one.
As per the last patch, if "struct page" is not power of 2,
early_hugetlb_free_vmemmap_param() does not set
hugetlb_free_vmemmap_enabled, so the "!is_power_of_2" check from above
would become useless here.
We know that in order for hugetlb_free_vmemmap_enabled to become true,
the is_power_of_2 must have succeed early on when calling the early_
function.

-- 
Oscar Salvador
SUSE L3