linux-kernel - Re: [PATCH v7 0/5] Free the 2nd vmemmap page associated with each HugeTLB page

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Date:   Wed, 10 Nov 2021 14:18:28 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com, Muchun Song <smuchun@...il.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        Barry Song <21cnbao@...il.com>,
        Chen Huang <chenhuang5@...wei.com>,
        "Bodeddula, Balasubramaniam" <bodeddub@...zon.com>
Subject: Re: [PATCH v7 0/5] Free the 2nd vmemmap page associated with each
 HugeTLB page

On Tue, Nov 9, 2021 at 3:33 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 11/8/21 12:16 AM, Muchun Song wrote:
> > On Mon, Nov 1, 2021 at 11:22 AM Muchun Song <songmuchun@...edance.com> wrote:
> >>
> >> This series can minimize the overhead of struct page for 2MB HugeTLB pages
> >> significantly. It further reduces the overhead of struct page by 12.5% for
> >> a 2MB HugeTLB compared to the previous approach, which means 2GB per 1TB
> >> HugeTLB. It is a nice gain. Comments and reviews are welcome. Thanks.
> >>
> >
> > Hi,
> >
> > Ping guys. Does anyone have any comments or suggestions
> > on this series?
> >
> > Thanks.
> >
>
> I did look over the series earlier.  I have no issue with the hugetlb and
> vmemmap modifications as they are enhancements to the existing
> optimizations.  My primary concern is the (small) increased overhead
> for the helpers as outlined in your cover letter.  Since these helpers
> are not limited to hugetlb and used throughout the kernel, I would
> really like to get comments from others with a better understanding of
> the potential impact.

Thanks Mike. I'd like to hear others' comments about this as well.
>From my point of view, maybe the (small) overhead is acceptable
since it only affects the head page, however Matthew Wilcox's folio
series could reduce this situation as well.

Looking forward to others' comments.

Thanks.

>
> --
> Mike Kravetz