linux-kernel - Re: [External] Re: [PATCH v10 00/11] Free some vmemmap pages of HugeTLB page

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Message-ID: <CAMZfGtX__Ys+ccGyMBYTO+i+0u+btaK1NF6tSafTP3B53zm+cg@mail.gmail.com>
Date:   Thu, 17 Dec 2020 23:52:09 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Oscar Salvador <osalvador@...e.de>
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>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>, naoya.horiguchi@....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 v10 00/11] Free some vmemmap pages of
 HugeTLB page

On Thu, Dec 17, 2020 at 11:00 PM Oscar Salvador <osalvador@...e.de> wrote:
>
> On Thu, Dec 17, 2020 at 08:12:52PM +0800, Muchun Song wrote:
> > In this case, for the 1GB HugeTLB page, we can save 4088 pages(There are
> > 4096 pages for struct page structs, we reserve 2 pages for vmemmap and 8
> > pages for page tables. So we can save 4088 pages). This is a very substantial
> > gain. On our server, run some SPDK/QEMU applications which will use 1024GB
> > hugetlbpage. With this feature enabled, we can save ~16GB(1G hugepage)/~11GB
> > (2MB hugepage, the worst case is 10GB while the best is 12GB) memory.
>
> Is the above really true?
> We no longer need to allocate pagetables, so the savings go up to 4094, right?

Yeah, you are right. I forget to update this.

>
> I will be off for a few days but I expect to get back to this and review the
> missing bits when I am back.
>

Thanks.

> --
> Oscar Salvador
> SUSE L3



-- 
Yours,
Muchun