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

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Message-Id: <20211123190952.7d1e0cac2d72acacd2df016c@linux-foundation.org>
Date:   Tue, 23 Nov 2021 19:09:52 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jonathan Corbet <corbet@....net>,
        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 Mon, 22 Nov 2021 12:21:32 +0800 Muchun Song <songmuchun@...edance.com> wrote:

> On Wed, Nov 10, 2021 at 2:18 PM Muchun Song <songmuchun@...edance.com> wrote:
> >
> > 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.

I think Mike was inviting you to run some tests to quantify the
overhead ;)

> Ping guys.
> 
> Hi Andrew,
> 
> Do you have any suggestions on this series to move it on?
> 

I tossed it in there for some testing but yes please, additional
reviewing?