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    Subject[RFC v8 PATCH 05/20] memory-hotplug: check whether memory is present or not
    Date
    From: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

    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.

    CC: David Rientjes <rientjes@google.com>
    CC: Jiang Liu <liuj97@gmail.com>
    CC: Len Brown <len.brown@intel.com>
    CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    CC: Paul Mackerras <paulus@samba.org>
    CC: Christoph Lameter <cl@linux.com>
    Cc: Minchan Kim <minchan.kim@gmail.com>
    CC: Andrew Morton <akpm@linux-foundation.org>
    CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    CC: Wen Congyang <wency@cn.fujitsu.com>
    Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    ---
    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 80cded7..3f1d7c5 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;
    --
    1.7.1


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