From: Dan Williams <dan.j.williams@intel.com>
To: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: 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>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section
Date: Wed, 24 Jun 2020 09:10:09 -0700 [thread overview]
Message-ID: <CAPcyv4gEUq0yyz00AbQQSyo_acj1wUCZPse5vEff_Bq7GmeksQ@mail.gmail.com> (raw)
In-Reply-To: <20200624061340.GA11552@L-31X9LVDL-1304.local>
On Tue, Jun 23, 2020 at 11:14 PM Wei Yang
<richard.weiyang@linux.alibaba.com> wrote:
>
> On Tue, Jun 23, 2020 at 05:18:28PM +0200, Michal Hocko wrote:
> >On Tue 23-06-20 17:42:58, Wei Yang wrote:
> >> For early sections, we assumes its memmap will never be partially
> >> removed. But current behavior breaks this.
> >>
> >> Let's correct it.
> >>
> >> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> >> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> >
> >Can a user trigger this or is this a theoretical bug?
>
> Let me rewrite the changelog a little. Look forward any comments.
>
> For early sections, its memmap is handled specially even sub-section is
> enabled. The memmap could only be populated as a whole.
>
> Quoted from the comment of section_activate():
>
> * The early init code does not consider partially populated
> * initial sections, it simply assumes that memory will never be
> * referenced. If we hot-add memory into such a section then we
> * do not need to populate the memmap and can simply reuse what
> * is already there.
>
> While current section_deactivate() breaks this rule. When hot-remove a
> sub-section, section_deactivate() would depopulate its memmap. The
> consequence is if we hot-add this subsection again, its memmap never get
> proper populated.
Ok, forgive the latency as re-fetched this logic into my mental cache.
So what I was remembering was the initial state of the code that
special cased early sections, and that still seems to be the case in
pfn_valid(). IIRC early_sections / bootmem are blocked from being
removed entirely. Partial / subsection removals are ok.
next prev parent reply other threads:[~2020-06-24 16:10 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 9:42 [PATCH] mm/spase: never partially remove memmap for early section Wei Yang
2020-06-23 12:44 ` David Hildenbrand
2020-06-23 13:02 ` Wei Yang
2020-06-23 13:16 ` David Hildenbrand
2020-06-23 15:18 ` Michal Hocko
2020-06-23 21:48 ` Wei Yang
2020-06-24 6:13 ` Wei Yang
2020-06-24 16:10 ` Dan Williams [this message]
2020-06-24 22:05 ` Wei Yang
2020-06-24 22:20 ` Dan Williams
2020-06-24 22:44 ` Wei Yang
2020-06-24 23:47 ` Dan Williams
2020-06-25 5:53 ` David Hildenbrand
2020-06-25 19:46 ` Dan Williams
2020-06-25 22:29 ` Wei Yang
2020-06-29 8:34 ` Wei Yang
2020-06-29 22:13 ` Dan Williams
2020-06-29 22:58 ` Wei Yang
2020-06-30 7:16 ` David Hildenbrand
2020-06-25 22:39 ` Wei Yang
2020-06-26 4:59 ` David Hildenbrand
2020-06-24 7:48 ` David Hildenbrand
2020-06-24 8:04 ` David Hildenbrand
2020-06-24 8:13 ` Wei Yang
2020-06-24 8:41 ` David Hildenbrand
2020-06-24 8:50 ` Michal Hocko
2020-06-24 22:27 ` Wei Yang
2020-06-24 0:21 ` Dan Williams
2020-06-24 1:11 ` Wei Yang
2020-06-24 1:47 ` Baoquan He
2020-06-24 2:14 ` Baoquan He
2020-06-24 3:46 ` Wei Yang
2020-06-24 3:52 ` Baoquan He
2020-06-24 3:56 ` Wei Yang
2020-06-24 8:51 ` David Hildenbrand
2020-06-24 22:08 ` Wei Yang
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