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

[Jaegeuk Hanse]

On 11/20/2012 05:37 PM, Wen Congyang wrote:
> At 11/20/2012 02:58 PM, Jaegeuk Hanse Wrote:
> > On 11/20/2012 02:55 PM, Wen Congyang wrote:
> > > At 11/20/2012 02:22 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,
> > > >
> > > > In order to review this patch, I should dig sparse memory codes in
> > > > advance. But I have some confuse of codes. Why need encode/decode mem
> > > > map instead of set mem_map to ms->section_mem_map directly?
> > > The memmap is aligned, and the low bits are zero. We store some
> > > information
> > > in these bits. So we need to encode/decode memmap here.
> > Hi Congyang,
> >
> > Thanks for you reponse. But I mean why return (unsigned long)(mem_map -
> > (section_nr_to_pfn(pnum))); in function sparse_encode_mem_map, and then
> > return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum); in
> > funtion sparse_decode_mem_map instead of just store mem_map in
> > ms->section_mep_map directly.
> I don't know why. I try to find the reason, but I don't find any
> place to use the pfn stored in the mem_map except in the decode
> function. Maybe the designer doesn't want us to access the mem_map
> directly.

It seems that mem_map is per node, but pfn is real pfn.
you can check __page_to_pfn.

> Thanks
> Wen Congyang
>
> > 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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