Re: [RFC v9 PATCH 05/21] memory-hotplug: check whether memory ispresent or not

[Yasuaki Ishimatsu]

Hi Wen,

2012/09/11 11:15, Wen Congyang wrote:
> Hi, ishimatsu
>
> At 09/05/2012 05:25 PM, wency@xxxxxxxxxxxxxx Wrote:
> > From: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> >
> > If system supports memory hot-remove, online_pages() may online removed pages.
> > So online_pages() need to check whether onlining pages are present or not.
>
> Because we use memory_block_change_state() to hotremoving memory, I think
> this patch can be removed. What do you think?

Pleae teach me detals a little more. If we use memory_block_change_state(),
does the conflict never occur? Why?

Thansk,
Yasuaki Ishimatsu

> Thanks
> Wen Congyang
>
> > CC: David Rientjes <rientjes@xxxxxxxxxx>
> > CC: Jiang Liu <liuj97@xxxxxxxxx>
> > CC: Len Brown <len.brown@xxxxxxxxx>
> > CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > CC: Paul Mackerras <paulus@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>
> > ---
> >   include/linux/mmzone.h |   19 +++++++++++++++++++
> >   mm/memory_hotplug.c    |   13 +++++++++++++
> >   2 files changed, 32 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index 2daa54f..ac3ae30 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1180,6 +1180,25 @@ void sparse_init(void);
> >   #define sparse_index_init(_sec, _nid)  do {} while (0)
> >   #endif /* CONFIG_SPARSEMEM */
> >
> > +#ifdef CONFIG_SPARSEMEM
> > +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
> > +{
> > +	int i;
> > +	for (i = 0; i < nr_pages; i++) {
> > +		if (pfn_present(pfn + i))
> > +			continue;
> > +		else
> > +			return -EINVAL;
> > +	}
> > +	return 0;
> > +}
> > +#else
> > +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
> > +{
> > +	return 0;
> > +}
> > +#endif /* CONFIG_SPARSEMEM*/
> > +
> >   #ifdef CONFIG_NODES_SPAN_OTHER_NODES
> >   bool early_pfn_in_nid(unsigned long pfn, int nid);
> >   #else
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 49f7747..299747d 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
> >   	struct memory_notify arg;
> >
> >   	lock_memory_hotplug();
> > +	/*
> > +	 * If system supports memory hot-remove, the memory may have been
> > +	 * removed. So we check whether the memory has been removed or not.
> > +	 *
> > +	 * Note: When CONFIG_SPARSEMEM is defined, pfns_present() become
> > +	 *       effective. If CONFIG_SPARSEMEM is not defined, pfns_present()
> > +	 *       always returns 0.
> > +	 */
> > +	ret = pfns_present(pfn, nr_pages);
> > +	if (ret) {
> > +		unlock_memory_hotplug();
> > +		return ret;
> > +	}
> >   	arg.start_pfn = pfn;
> >   	arg.nr_pages = nr_pages;
> >   	arg.status_change_nid = -1;


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