From: Michal Hocko <mhocko@kernel.org>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, richardw.yang@linux.intel.com,
david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
rppt@linux.ibm.com, robin.murphy@arm.com
Subject: Re: [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case
Date: Wed, 26 Feb 2020 10:10:18 +0100 [thread overview]
Message-ID: <20200226091018.GD3771@dhcp22.suse.cz> (raw)
In-Reply-To: <20200226035336.GF24216@MiWiFi-R3L-srv>
On Wed 26-02-20 11:53:36, Baoquan He wrote:
> On 02/25/20 at 10:57am, Michal Hocko wrote:
> > On Thu 20-02-20 12:33:13, Baoquan He wrote:
> > > Currently, subsection map is used when SPARSEMEM is enabled, including
> > > VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not
> > > supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary
> > > and misleading. Let's adjust code to only allow subsection map being
> > > used in VMEMMAP case.
> >
> > This really needs more explanation I believe. What exactly happens if
> > somebody tries to hotremove a part of the section with !VMEMMAP? I can
> > see that clear_subsection_map returns 0 but that is not an error code.
> > Besides that section_deactivate doesn't propagate the error upwards.
> > /me stares into the code
> >
> > OK, I can see it now. It is relying on check_pfn_span to use the proper
> > subsection granularity. This really begs for a comment in the code
> > somewhere.
>
> Yes, check_pfn_span() guards it. People have no way to hot add/remove
> on non-section aligned block with !VMEMMAP.
>
> I have added extra comment to above section_activate() to note this,
> please check patch 5/7. Let me see how to add words to reflect the
> check_pfn_span() guard thing.
An explicit note about check_pfn_span gating the proper alignement and
sizing sounds sufficient to me.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-02-26 9:10 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 4:33 [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Baoquan He
2020-02-20 4:33 ` [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case Baoquan He
2020-02-20 6:11 ` Wei Yang
2020-02-20 12:07 ` David Hildenbrand
2020-02-26 12:31 ` David Hildenbrand
2020-02-26 13:07 ` Baoquan He
2020-02-26 18:09 ` Dan Williams
2020-02-26 18:09 ` Dan Williams
2020-03-03 8:34 ` David Hildenbrand
2020-03-03 8:39 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 2/7] mm/sparse.c: introduce new function fill_subsection_map() Baoquan He
2020-02-20 6:14 ` Wei Yang
2020-02-28 14:27 ` David Hildenbrand
2020-03-01 4:59 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection_map() Baoquan He
2020-02-20 6:15 ` Wei Yang
2020-02-28 14:36 ` David Hildenbrand
2020-03-01 5:20 ` Baoquan He
2020-03-02 15:43 ` David Hildenbrand
2020-03-03 1:53 ` Baoquan He
2020-03-03 8:22 ` Baoquan He
2020-03-03 8:33 ` David Hildenbrand
2020-03-03 8:38 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case Baoquan He
2020-02-20 6:17 ` Wei Yang
2020-02-25 9:57 ` Michal Hocko
2020-02-26 3:53 ` Baoquan He
2020-02-26 9:10 ` Michal Hocko [this message]
2020-02-28 7:25 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 5/7] mm/sparse.c: add code comment about sub-section hotplug Baoquan He
2020-02-20 4:33 ` [PATCH v2 6/7] mm/sparse.c: move subsection_map related codes together Baoquan He
2020-02-20 6:18 ` Wei Yang
2020-02-20 7:04 ` Baoquan He
2020-02-20 7:12 ` Wei Yang
2020-02-20 8:55 ` Baoquan He
2020-02-20 21:52 ` Wei Yang
2020-02-20 4:33 ` [PATCH v2 7/7] mm/sparse.c: Use __get_free_pages() instead in populate_section_memmap() Baoquan He
2020-02-20 10:38 ` [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Michal Hocko
2020-02-21 14:28 ` Baoquan He
2020-02-25 9:10 ` David Hildenbrand
2020-02-25 10:02 ` Michal Hocko
2020-02-26 3:42 ` Baoquan He
2020-02-26 9:14 ` Michal Hocko
2020-02-26 12:30 ` Baoquan He
2020-02-25 10:03 ` Michal Hocko
2020-02-26 3:44 ` Baoquan He
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