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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Mon, 25 Jan 2021 20:31:31 +0800
Message-ID: <CAMZfGtWaBSA7yHD218h0p_5+9OgCveYemF6xn3cKA6SopjhjVQ@mail.gmail.com>
Subject: Re: [External] Re: [PATCH v13 09/12] mm: hugetlb: add a kernel
 parameter hugetlb_free_vmemmap
To:     Oscar Salvador <osalvador@suse.de>
Cc:     David Hildenbrand <david@redhat.com>,
        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>,
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        <naoya.horiguchi@nec.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>
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On Mon, Jan 25, 2021 at 8:08 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Mon, Jan 25, 2021 at 12:43:23PM +0100, David Hildenbrand wrote:
> > > -   if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> > > +   if (is_hugetlb_free_vmemmap_enabled() ||
> > > +       end - start < PAGES_PER_SECTION * sizeof(struct page))
> >
> > This looks irresponsible. You ignore any altmap, even though current
> > altmap users (ZONE_DEVICE) will not actually result in applicable
> > vmemmaps that huge pages could ever use.
> >
> > Why do you ignore the altmap completely? This has to be properly
> > documented, but IMHO it's not even the right approach to mess with
> > altmap here.
>
> The goal was not to ignore altmap but to disable PMD mapping sections
> when the feature was enabled.
> Shame on me I did not notice that with this, altmap will be ignored.
>
> Something like below maybe:

Yeah, Thanks a lot.

>
> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>                 struct vmem_altmap *altmap)
> {
>         int err;
>         bool populate_base_pages = false;
>
>         if ((end - start < PAGES_PER_SECTION * sizeof(struct page)) ||
>             (is_hugetlb_free_vmemmap_enabled() && !altmap))
>                 populate_base_pages = true;
>
>         if (populate_base_pages) {
>                 err = vmemmap_populate_basepages(start, end, node, NULL);
>         } else if (boot_cpu_has(X86_FEATURE_PSE)) {
>         ....
>
>
> >
> > --
> > Thanks,
> >
> > David / dhildenb
> >
> >
>
> --
> Oscar Salvador
> SUSE L3