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

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Message-ID: <bcd9b0c8b5b34fb7bcfc97328d9d3dde@hisilicon.com>
Date:   Wed, 18 Nov 2020 03:27:56 +0000
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>
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Subject: RE: [External] RE: [PATCH v4 00/21] Free some vmemmap pages of
 hugetlb page



> -----Original Message-----
> From: Oscar Salvador [mailto:osalvador@...e.de]
> Sent: Wednesday, November 18, 2020 8:45 AM
> To: Muchun Song <songmuchun@...edance.com>
> Cc: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>;
> corbet@....net; mike.kravetz@...cle.com; tglx@...utronix.de;
> mingo@...hat.com; bp@...en8.de; x86@...nel.org; hpa@...or.com;
> dave.hansen@...ux.intel.com; luto@...nel.org; peterz@...radead.org;
> viro@...iv.linux.org.uk; akpm@...ux-foundation.org; paulmck@...nel.org;
> mchehab+huawei@...nel.org; pawan.kumar.gupta@...ux.intel.com;
> rdunlap@...radead.org; oneukum@...e.com; anshuman.khandual@....com;
> jroedel@...e.de; almasrymina@...gle.com; rientjes@...gle.com;
> willy@...radead.org; mhocko@...e.com; duanxiongchun@...edance.com;
> linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> linux-fsdevel@...r.kernel.org
> Subject: Re: [External] RE: [PATCH v4 00/21] Free some vmemmap pages of
> hugetlb page
> 
> 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.

Yep. I am not expecting freeing tail page to be done at this stage. This could
be something in the todo list after the first patchset is solid.

> 
> --
> Oscar Salvador
> SUSE L3

Thanks
Barry