Re: [External] Re: [PATCH v8 09/12] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap

From: Muchun Song <songmuchun@bytedance.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	viro@zeniv.linux.org.uk,
	Andrew Morton <akpm@linux-foundation.org>,
	paulmck@kernel.org, mchehab+huawei@kernel.org,
	pawan.kumar.gupta@linux.intel.com,
	Randy Dunlap <rdunlap@infradead.org>,
	oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
	Mina Almasry <almasrymina@google.com>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@suse.com>,
	"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	David Hildenbrand <david@redhat.com>,
	Xiongchun duan <duanxiongchun@bytedance.com>,
	linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v8 09/12] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap
Date: Thu, 10 Dec 2020 20:26:28 +0800	[thread overview]
Message-ID: <CAMZfGtVks41ZXaUgPdLyNqVCRYTvSm5qAN9GM5e0vqJ9YV7NdA@mail.gmail.com> (raw)
In-Reply-To: <20201210100454.GB3613@localhost.localdomain>

On Thu, Dec 10, 2020 at 7:41 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> 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

Thanks.

>
> > -     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

Well, I can do it.

>
> >       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.

Agree. The condition does not need to be rechecked.
Will  do in the next version. Thanks.

>
> > +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.
>

Thanks.

>
> --
> Oscar Salvador
> SUSE L3

-- 
Yours,
Muchun