linux-kernel - Re: [PATCH v9 11/11] mm/hugetlb: Optimize the code with the help of the compiler

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Date:   Thu, 17 Dec 2020 11:31:59 +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 v9 11/11] mm/hugetlb: Optimize the code with the help of
 the compiler

On Sun, Dec 13, 2020 at 11:45:34PM +0800, Muchun Song wrote:
>  static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
>  {
> -	return h->nr_free_vmemmap_pages;
> +	return h->nr_free_vmemmap_pages && is_power_of_2(sizeof(struct page));

This is wrong as it will return either true or false, but not what we want:

	static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
	{
	        return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
	}

the above will compute to 4096, which is wrong for obvious reasons.

-- 
Oscar Salvador
SUSE L3