linux-kernel - Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

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Date:   Wed, 9 Dec 2020 18:03:02 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk,
        Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org,
        mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com,
        Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com,
        anshuman.khandual@....com, jroedel@...e.de,
        Mina Almasry <almasrymina@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing
 vmemmap if struct page size is not power of two

On Wed, Dec 9, 2020 at 5:57 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 30.11.20 16:18, Muchun Song wrote:
> > We only can free the tail vmemmap pages of HugeTLB to the buddy allocator
> > when the size of struct page is a power of two.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > ---
> >  mm/hugetlb_vmemmap.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index 51152e258f39..ad8fc61ea273 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -111,6 +111,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> >       unsigned int nr_pages = pages_per_huge_page(h);
> >       unsigned int vmemmap_pages;
> >
> > +     if (!is_power_of_2(sizeof(struct page))) {
> > +             pr_info("disable freeing vmemmap pages for %s\n", h->name);
>
> I'd just drop that pr_info(). Users are able to observe that it's
> working (below), so they are able to identify that it's not working as well.

The below is just a pr_debug. Do you suggest converting it to pr_info?

>
> > +             return;
> > +     }
> > +
> >       vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
> >       /*
> >        * The head page and the first tail page are not to be freed to buddy
> >
>
> Please squash this patch into the enabling patch and add a comment
> instead, like
>
> /* We cannot optimize if a "struct page" crosses page boundaries. */
>

Will do. Thanks.

> --
> Thanks,
>
> David / dhildenb
>


-- 
Yours,
Muchun