linux-kernel - Re: [External] Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

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Message-ID: <CAMZfGtWgfhS=ZfmA1wyaGWC=9bMo01-i13OKmhofL0-CX0TLkQ@mail.gmail.com>
Date:   Thu, 11 Mar 2021 16:49:24 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <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>,
        Alexander Viro <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>,
        Oscar Salvador <osalvador@...e.de>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>,
        Joao Martins <joao.m.martins@...cle.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>,
        Chen Huang <chenhuang5@...wei.com>,
        Bodeddula Balasubramaniam <bodeddub@...zon.com>
Subject: Re: [External] Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap
 pages associated with each HugeTLB page

On Thu, Mar 11, 2021 at 4:46 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Thu 11-03-21 12:26:32, Muchun Song wrote:
> > On Wed, Mar 10, 2021 at 11:19 PM Michal Hocko <mhocko@...e.com> wrote:
> > >
> > > On Mon 08-03-21 18:28:02, Muchun Song wrote:
> [...]
> > > > @@ -1771,8 +1813,12 @@ int dissolve_free_huge_page(struct page *page)
> > > >               h->free_huge_pages--;
> > > >               h->free_huge_pages_node[nid]--;
> > > >               h->max_huge_pages--;
> > > > -             update_and_free_page(h, head);
> > > > -             rc = 0;
> > > > +             rc = update_and_free_page(h, head);
> > > > +             if (rc) {
> > > > +                     h->surplus_huge_pages--;
> > > > +                     h->surplus_huge_pages_node[nid]--;
> > > > +                     h->max_huge_pages++;
> > >
> > > This is quite ugly and confusing. update_and_free_page is careful to do
> > > the proper counters accounting and now you just override it partially.
> > > Why cannot we rely on update_and_free_page do the right thing?
> >
> > Dissolving path is special here. Since update_and_free_page failed,
> > the number of surplus pages was incremented.  Surplus pages are
> > the number of pages greater than max_huge_pages.  Since we are
> > incrementing max_huge_pages, we should decrement (undo) the
> > addition to surplus_huge_pages and surplus_huge_pages_node[nid].
>
> Can we make dissolve_free_huge_page less special or tell
> update_and_free_page to not account against dissolve_free_huge_page?

Of course can.

Thanks.

> --
> Michal Hocko
> SUSE Labs