From: Dan Williams <dan.j.williams@intel.com>
To: David Hildenbrand <david@redhat.com>
Cc: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"mhocko@kernel.org" <mhocko@kernel.org>,
"adobriyan@gmail.com" <adobriyan@gmail.com>,
"hch@lst.de" <hch@lst.de>,
"longman@redhat.com" <longman@redhat.com>,
"sfr@canb.auug.org.au" <sfr@canb.auug.org.au>,
"mst@redhat.com" <mst@redhat.com>, "cai@lca.pw" <cai@lca.pw>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Junichi Nomura <j-nomura@ce.jp.nec.com>
Subject: Re: [PATCH 2/3] mm: Introduce subsection_dev_map
Date: Wed, 13 Nov 2019 13:11:46 -0800 [thread overview]
Message-ID: <CAPcyv4gpN8kbh1i6jCDdC2OP41G3C2+7YD4rYz-3HaD_pufvyg@mail.gmail.com> (raw)
In-Reply-To: <28CEC8B8-AC6A-4A13-B5A4-C47DB64B45E6@redhat.com>
On Wed, Nov 13, 2019 at 12:40 PM David Hildenbrand <david@redhat.com> wrote:
[..]
> >>>> I'm still struggling to understand the motivation of distinguishing
> >>>> "active" as something distinct from "online". As long as the "online"
> >>>> granularity is improved from sections down to subsections then most
> >>>> code paths are good to go. The others can use get_devpagemap() to
> >>>> check for ZONE_DEVICE in a race free manner as they currently do.
> >>>
> >>> I thought we wanted to unify access if we don’t really care about the zone as in most pfn walkers - E.g., for zone shrinking.
> >>
> >> Agree, when the zone does not matter, which is most cases, then
> >> pfn_online() and pfn_valid() are sufficient.
>
> Oh, and just to clarify why I proposed pfn_active(): The issue right now is that a PFN that is valid but not online could be offline memory (memmap not initialized) or ZONE_DEVICE. That‘s why I wanted to have a way to detect if a memmap was initialized, independent of the zone. That‘s important for generic PFN walkers.
That's what I was debating with Toshiki [1], whether there is a real
example of needing to distinguish ZONE_DEVICE from offline memory in a
pfn walker. The proposed use case in this patch set of being able to
set hwpoison on ZONE_DEVICE pages does not seem like a good idea to
me. My suspicion is that this is a common theme and others are looking
to do these types page manipulations that only make sense for online
memory. If that is the case then treating ZONE_DEVICE as offline seems
the right direction.
[1]: https://lore.kernel.org/linux-mm/CAPcyv4joVDwiL21PPyJ7E_mMFR2SL3QTi09VMtfxb_W+-1p8vQ@mail.gmail.com/
next prev parent reply other threads:[~2019-11-13 21:11 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 0:08 [PATCH 0/3] make pfn walker support ZONE_DEVICE Toshiki Fukasawa
2019-11-08 0:08 ` [PATCH 1/3] procfs: refactor kpage_*_read() in fs/proc/page.c Toshiki Fukasawa
2019-11-08 0:08 ` [PATCH 2/3] mm: Introduce subsection_dev_map Toshiki Fukasawa
2019-11-08 19:13 ` Dan Williams
2019-11-13 18:51 ` David Hildenbrand
2019-11-13 19:06 ` Dan Williams
2019-11-13 19:53 ` David Hildenbrand
2019-11-13 20:10 ` Dan Williams
2019-11-13 20:23 ` David Hildenbrand
2019-11-13 20:40 ` David Hildenbrand
2019-11-13 21:11 ` Dan Williams [this message]
2019-11-13 21:22 ` David Hildenbrand
2019-11-13 21:26 ` Dan Williams
2019-11-14 23:36 ` Toshiki Fukasawa
2019-11-15 0:46 ` David Hildenbrand
2019-11-15 2:57 ` Toshiki Fukasawa
2019-11-08 0:08 ` [PATCH 3/3] mm: make pfn walker support ZONE_DEVICE Toshiki Fukasawa
2019-11-09 17:08 ` kbuild test robot
2019-11-09 19:14 ` kbuild test robot
2019-11-08 9:18 ` [PATCH 0/3] " Michal Hocko
2019-11-11 8:00 ` Toshiki Fukasawa
2019-11-11 16:23 ` Dan Williams
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