Re: [PATCH v3 06/12] memory-hotplug: unregister memory section onSPARSEMEM_VMEMMAP

[Jaegeuk Hanse]

On 11/21/2012 11:05 AM, Wen Congyang wrote:
> At 11/20/2012 07:16 PM, Jaegeuk Hanse Wrote:
> > On 11/01/2012 05:44 PM, Wen Congyang wrote:
> > > From: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> > >
> > > Currently __remove_section for SPARSEMEM_VMEMMAP does nothing. But
> > > even if
> > > we use SPARSEMEM_VMEMMAP, we can unregister the memory_section.
> > >
> > > So the patch add unregister_memory_section() into __remove_section().
> > Hi Yasuaki,
> >
> > I have a question about these sparse vmemmap memory related patches. Hot
> > add memory need allocated vmemmap pages, but this time is allocated by
> > buddy system. How can gurantee virtual address is continuous to the
> > address allocated before? If not continuous, page_to_pfn and pfn_to_page
> > can't work correctly.
> vmemmap has its virtual address range:
> ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
>
> We allocate memory from buddy system to store struct page, and its virtual
> address isn't in this range. So we should update the page table:
>
> kmalloc_section_memmap()
>      sparse_mem_map_populate()
>          pfn_to_page() // get the virtual address in the vmemmap range
>          vmemmap_populate() // we update page table here
>
> When we use vmemmap, page_to_pfn() always returns address in the vmemmap
> range, not the address that kmalloc() returns. So the virtual address
> is continuous.

Hi Congyang,

Another question about memory hotplug. During hot remove memory, it will 
also call memblock_remove to remove related memblock.
memblock_remove()
           __memblock_remove()
                   memblock_isolate_range()
                   memblock_remove_region()

But memblock_isolate_range() only record fully contained regions, 
regions which are partial overlapped just be splitted instead of record. 
So these partial overlapped regions can't be removed. Where I miss?

Regards,
Jaegeuk

> Thanks
> Wen Congyang
> > Regards,
> > Jaegeuk
> >
> > > CC: David Rientjes <rientjes@xxxxxxxxxx>
> > > CC: Jiang Liu <liuj97@xxxxxxxxx>
> > > CC: Len Brown <len.brown@xxxxxxxxx>
> > > CC: Christoph Lameter <cl@xxxxxxxxx>
> > > Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> > > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> > > CC: Wen Congyang <wency@xxxxxxxxxxxxxx>
> > > Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> > > ---
> > >    mm/memory_hotplug.c | 13 ++++++++-----
> > >    1 file changed, 8 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > > index ca07433..66a79a7 100644
> > > --- a/mm/memory_hotplug.c
> > > +++ b/mm/memory_hotplug.c
> > > @@ -286,11 +286,14 @@ static int __meminit __add_section(int nid,
> > > struct zone *zone,
> > >    #ifdef CONFIG_SPARSEMEM_VMEMMAP
> > >    static int __remove_section(struct zone *zone, struct mem_section *ms)
> > >    {
> > > -    /*
> > > -     * XXX: Freeing memmap with vmemmap is not implement yet.
> > > -     *      This should be removed later.
> > > -     */
> > > -    return -EBUSY;
> > > +    int ret = -EINVAL;
> > > +
> > > +    if (!valid_section(ms))
> > > +        return ret;
> > > +
> > > +    ret = unregister_memory_section(ms);
> > > +
> > > +    return ret;
> > >    }
> > >    #else
> > >    static int __remove_section(struct zone *zone, struct mem_section *ms)

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