linux-kernel - Re: [PATCH v8 09/12] mm/hugetlb: Add a kernel parameter hugetlb_free

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Message-ID: <20201210100454.GB3613@localhost.localdomain>
Date:   Thu, 10 Dec 2020 11:04:54 +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 09/12] mm/hugetlb: Add a kernel parameter
 hugetlb_free_vmemmap

On Thu, Dec 10, 2020 at 11:55:23AM +0800, Muchun Song wrote:
> +hugetlb_free_vmemmap
> +	When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing
> +	unused vmemmap pages associated each HugeTLB page.
                                      ^^^ with

> -	if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> +	if (is_hugetlb_free_vmemmap_enabled())
> +		err = vmemmap_populate_basepages(start, end, node, NULL);
> +	else if (end - start < PAGES_PER_SECTION * sizeof(struct page))
>  		err = vmemmap_populate_basepages(start, end, node, NULL);

Not sure if joining those in an OR makes se.se

>  	else if (boot_cpu_has(X86_FEATURE_PSE))
>  		err = vmemmap_populate_hugepages(start, end, node, altmap);
> @@ -1610,7 +1613,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,
>  		}
>  		get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO);
>  
> -		if (!boot_cpu_has(X86_FEATURE_PSE)) {
> +		if (!boot_cpu_has(X86_FEATURE_PSE) ||
> +		    is_hugetlb_free_vmemmap_enabled()) {

I would add a variable at the beginning called "basepages_populated"
that holds the result of those two conditions.
I am not sure if it slightly improves the code as the conditions do
not need to be rechecked, but the readibility a bit.

> +bool hugetlb_free_vmemmap_enabled;
> +
> +static int __init early_hugetlb_free_vmemmap_param(char *buf)
> +{
> +	if (!buf)
> +		return -EINVAL;
> +
> +	/* We cannot optimize if a "struct page" crosses page boundaries. */

I think this comment belongs to the last patch.


-- 
Oscar Salvador
SUSE L3