Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
From:   David Hildenbrand <david@redhat.com>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section
Date:   Fri, 26 Jun 2020 06:59:11 +0200
Message-Id: <5CA8ECA1-2360-4AAA-954F-931404EFEB2B@redhat.com>
References: <20200625223952.GA17926@L-31X9LVDL-1304.local>
Cc:     David Hildenbrand <david@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Linux MM <linux-mm@kvack.org>, Baoquan He <bhe@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <20200625223952.GA17926@L-31X9LVDL-1304.local>
To:     Wei Yang <richard.weiyang@linux.alibaba.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Am 26.06.2020 um 00:40 schrieb Wei Yang <richard.weiyang@linux.alibaba.com=
>:
>=20
> =EF=BB=BFOn Thu, Jun 25, 2020 at 07:53:37AM +0200, David Hildenbrand wrote=
:
>>=20
>>=20
>>>> Am 25.06.2020 um 01:47 schrieb Dan Williams <dan.j.williams@intel.com>:=

>>>=20
>>> =EF=BB=BFOn Wed, Jun 24, 2020 at 3:44 PM Wei Yang
>>> <richard.weiyang@linux.alibaba.com> wrote:
>>> [..]
>>>>> So, you are right that there is a mismatch here, but I think the
>>>>> comprehensive fix is to allow early sections to be partially
>>>>> depopulated/repopulated rather than have section_activate() and
>>>>> section_deacticate() special case early sections. The special casing
>>>>> is problematic in retrospect as section_deactivate() can't be
>>>>> maintained without understand special rules in section_activate().
>>>>=20
>>>> Hmm... This means we need to adjust pfn_valid() too, which always retur=
n true
>>>> for early sections.
>>>=20
>>> Right, rather than carry workarounds in 3 locations, and the bug that
>>> has resulted from then getting out of sync, just teach early section
>>> mapping to allow for the subsection populate/depopulate.
>>>=20
>>=20
>> I prefer the easy fix first - IOW what we Here here. Especially, pfn_to_o=
nline_page() will need changes as well.
>>=20
>=20
> Hi, David,
>=20
> Which part of pfn_to_online_page() needs to be changed? pfn_valid_within()=

> would call pfn_valid() to check the pfn first. This looks enough for me.

Not for all configurations. For some (e.g., x86 iirc) it=E2=80=98s just a no=
p.=