linux-kernel - Re: [External] Re: [PATCH v18 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem

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Date:   Thu, 11 Mar 2021 17:05:15 +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>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Chen Huang <chenhuang5@...wei.com>,
        Bodeddula Balasubramaniam <bodeddub@...zon.com>
Subject: Re: [External] Re: [PATCH v18 1/9] mm: memory_hotplug: factor out
 bootmem core functions to bootmem_info.c

On Thu, Mar 11, 2021 at 4:53 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Thu 11-03-21 16:45:51, Muchun Song wrote:
> > On Thu, Mar 11, 2021 at 10:58 AM Muchun Song <songmuchun@...edance.com> wrote:
> > >
> > > On Wed, Mar 10, 2021 at 10:14 PM Michal Hocko <mhocko@...e.com> wrote:
> > > >
> > > > [I am sorry for a late review]
> > >
> > > Thanks for your review.
> > >
> > > >
> > > > On Mon 08-03-21 18:27:59, Muchun Song wrote:
> > > > > Move bootmem info registration common API to individual bootmem_info.c.
> > > > > And we will use {get,put}_page_bootmem() to initialize the page for the
> > > > > vmemmap pages or free the vmemmap pages to buddy in the later patch.
> > > > > So move them out of CONFIG_MEMORY_HOTPLUG_SPARSE. This is just code
> > > > > movement without any functional change.
> > > > >
> > > > > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > > > > Acked-by: Mike Kravetz <mike.kravetz@...cle.com>
> > > > > Reviewed-by: Oscar Salvador <osalvador@...e.de>
> > > > > Reviewed-by: David Hildenbrand <david@...hat.com>
> > > > > Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>
> > > > > Tested-by: Chen Huang <chenhuang5@...wei.com>
> > > > > Tested-by: Bodeddula Balasubramaniam <bodeddub@...zon.com>
> > > >
> > > > Separation from memory_hotplug.c is definitely a right step. I am
> > > > wondering about the config dependency though
> > > > [...]
> > > > > diff --git a/mm/Makefile b/mm/Makefile
> > > > > index 72227b24a616..daabf86d7da8 100644
> > > > > --- a/mm/Makefile
> > > > > +++ b/mm/Makefile
> > > > > @@ -83,6 +83,7 @@ obj-$(CONFIG_SLUB) += slub.o
> > > > >  obj-$(CONFIG_KASAN)  += kasan/
> > > > >  obj-$(CONFIG_KFENCE) += kfence/
> > > > >  obj-$(CONFIG_FAILSLAB) += failslab.o
> > > > > +obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
> > > >
> > > > I would have expected this would depend on CONFIG_SPARSE.
> > > > BOOTMEM_INFO_NODE is really an odd thing to depend on here. There is
> > > > some functionality which requires the node info but that can be gated
> > > > specifically. Or what is the thinking behind?
> >
> > I have tried this. And I find that it is better to depend on
> > BOOTMEM_INFO_NODE instead of SPARSEMEM.
> >
> > If we enable SPARSEMEM but disable HAVE_BOOTMEM_INFO_NODE,
> > the bootmem_info.c also is compiled. Actually, we do not
> > need those functions on other architectures. And these
> > functions are also related to bootmem info. So it may be
> > more reasonable to depend on BOOTMEM_INFO_NODE.
> > Just my thoughts.
>
> If BOOTMEM_INFO_NODE is disbabled then bootmem_info.c would be
> effectivelly only {get,put}_page_bootmem, no?

{get,put}_page_bootmem also would be effective. I found that
get_page_bootmem is only used in the scope of the
CONFIG_BOOTMEM_INFO_NODE. So I move them
to the bootmem_info.c.

Thanks.

>
> --
> Michal Hocko
> SUSE Labs