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From: Baoquan He <bhe@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
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: Fri, 28 Feb 2020 15:25:36 +0800	[thread overview]
Message-ID: <20200228072536.GK24216@MiWiFi-R3L-srv> (raw)
In-Reply-To: <20200226091018.GD3771@dhcp22.suse.cz>

On 02/26/20 at 10:10am, Michal Hocko wrote:
> 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.

It's fine to me, I will adjust the description.



  reply	other threads:[~2020-02-28  7:25 UTC|newest]

Thread overview: 45+ 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
2020-03-03  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
2020-02-28  7:25         ` Baoquan He [this message]
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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