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From: Baoquan He <bhe@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <osalvador@suse.de>, Linux MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn
Date: Fri, 7 Feb 2020 11:10:11 +0800	[thread overview]
Message-ID: <20200207031011.GR8965@MiWiFi-R3L-srv> (raw)
In-Reply-To: <CAPcyv4h7dKE85EQ9jR1akXnT6PcG2M2g7YCCLqse=kKieP1H9w@mail.gmail.com>

Hi Dan,

On 02/06/20 at 06:19pm, Dan Williams wrote:
> On Thu, Feb 6, 2020 at 3:17 PM Wei Yang <richardw.yang@linux.intel.com> wrote:
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index b5da121bdd6e..56816f653588 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -888,7 +888,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> >         /* Align memmap to section boundary in the subsection case */
> >         if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
> >                 section_nr_to_pfn(section_nr) != start_pfn)
> > -               memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr));
> > +               memmap = pfn_to_page(section_nr_to_pfn(section_nr));
> 
> Yes, this looks obviously correct. This might be tripping up
> makedumpfile. Do you see any practical effects of this bug? The kernel
> mostly avoids ->section_mem_map in the vmemmap case and in the
> !vmemmap case section_nr_to_pfn(section_nr) should always equal
> start_pfn.

The practical effects is that the memmap for the first unaligned section will be lost
when destroy namespace to hot remove it. Because we encode the ->section_mem_map
into mem_section, and get memmap from the related mem_section to free it in
section_deactivate(). In fact in vmemmap, we don't need to encode the ->section_mem_map
with memmap.

By the way, sub-section support is only valid in vmemmap case, right?
Seems yes from code, but I don't find any document to prove it.

Thanks
Baoquan


  reply	other threads:[~2020-02-07  3:10 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-06 23:16 [PATCH 0/3] Fixes "mm/sparsemem: support sub-section hotplug" Wei Yang
2020-02-06 23:16 ` [PATCH 1/3] mm/sparsemem: adjust memmap only for SPARSEMEM_VMEMMAP Wei Yang
2020-02-07  2:00   ` Dan Williams
2020-02-07 11:06     ` Wei Yang
2020-02-06 23:16 ` [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn Wei Yang
2020-02-07  2:19   ` Dan Williams
2020-02-07  3:10     ` Baoquan He [this message]
2020-02-07  3:21       ` Dan Williams
2020-02-07  3:36         ` Baoquan He
2020-02-07  4:05           ` Dan Williams
2020-02-07 11:13           ` Wei Yang
2020-02-07 12:14         ` Wei Yang
2020-02-07 16:44           ` Dan Williams
2020-02-07 10:51     ` Wei Yang
2020-02-07 11:26     ` Wei Yang
2020-02-09 13:50       ` Baoquan He
2020-02-09 14:14         ` David Hildenbrand
2020-02-10  0:36           ` Wei Yang
2020-02-07  4:11   ` Baoquan He
2020-02-07 10:53     ` Wei Yang
2020-02-06 23:16 ` [PATCH 3/3] mm/sparsemem: avoid memmap overwrite for non-SPARSEMEM_VMEMMAP Wei Yang
2020-02-07  2:06   ` Dan Williams
2020-02-07  3:50     ` Baoquan He
2020-02-07 11:02     ` Wei Yang

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