linux-kernel - Re: [External] RE: [PATCH v4 00/21] Free some vmemmap pages of hugetlb page

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Message-ID: <CAMZfGtWMF7ZbPHOZg69VNNO0oiVf=i3pAEVmwsmV32wpbAHYxw@mail.gmail.com>
Date:   Wed, 18 Nov 2020 11:27:50 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        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>,
        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 v4 00/21] Free some vmemmap pages of
 hugetlb page

On Wed, Nov 18, 2020 at 3:45 AM Oscar Salvador <osalvador@...e.de> wrote:
>
> On 2020-11-17 17:29, Muchun Song wrote:
> > Now for the 2MB HugrTLB page, we only free 6 vmemmap pages.
> > But your words woke me up. Maybe we really can free 7 vmemmap
> > pages. In this case, we can see 8 of the 512 struct page structures
> > has beed set PG_head flag. If we can adjust compound_head()
> > slightly and make compound_head() return the real head struct
> > page when the parameter is the tail struct page but with PG_head
> > flag set. I will start an investigation and a test.
>
> I would not overcomplicate things at this stage, but rather keep it
> simple as the code is already tricky enough(without counting the LOC
> thatvit adds).
> We can always build on top later on in order to improve things.

I think that this improvement can be a separate patch. In this case,
it can make the code evolution route clearer.

Thanks.


>
> --
> Oscar Salvador
> SUSE L3



-- 
Yours,
Muchun