[Xen-devel] [PATCH V2 2/2] mm: Extend memory hotplug API to allow memory hotplug in virtual machines

[Daniel Kiper <dkiper@xxxxxxxxxxxx>]

This patch contains online_page_callback and apropriate functions for
registering/unregistering online page callbacks. It allows to do some
machine specific tasks during online page stage which is required
to implement memory hotplug in virtual machines. Additionally,
__online_page_set_limits(), __online_page_increment_counters() and
__online_page_free() function was added to ease generic
hotplug operation.

Signed-off-by: Daniel Kiper <dkiper@xxxxxxxxxxxx>
---
 include/linux/memory_hotplug.h |   11 +++++-
 mm/memory_hotplug.c            |   68 ++++++++++++++++++++++++++++++++++++++--
 2 files changed, 74 insertions(+), 5 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 8122018..014bd96 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -68,12 +68,19 @@ static inline void zone_seqlock_init(struct zone *zone)
 extern int zone_grow_free_lists(struct zone *zone, unsigned long new_nr_pages);
 extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
 extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
-/* need some defines for these for archs that don't support it */
-extern void online_page(struct page *page);
 /* VM interface that may be used by firmware interface */
 extern int online_pages(unsigned long, unsigned long);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
 
+typedef void (*online_page_callback_t)(struct page *page);
+
+extern int register_online_page_callback(online_page_callback_t callback);
+extern int unregister_online_page_callback(online_page_callback_t callback);
+
+extern void __online_page_set_limits(struct page *page);
+extern void __online_page_increment_counters(struct page *page);
+extern void __online_page_free(struct page *page);
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 extern bool is_pageblock_removable_nolock(struct page *page);
 #endif /* CONFIG_MEMORY_HOTREMOVE */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a807ccb..6bf78be 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -34,6 +34,17 @@
 
 #include "internal.h"
 
+/*
+ * online_page_callback contains pointer to current page onlining function.
+ * Initially it is generic_online_page(). If it is required it could be
+ * changed by calling register_online_page_callback() for callback registration
+ * and unregister_online_page_callback() for callback unregistration.
+ */
+
+static void generic_online_page(struct page *page);
+
+static online_page_callback_t online_page_callback = generic_online_page;
+
 DEFINE_MUTEX(mem_hotplug_mutex);
 
 void lock_memory_hotplug(void)
@@ -361,23 +372,74 @@ int __remove_pages(struct zone *zone, unsigned long 
phys_start_pfn,
 }
 EXPORT_SYMBOL_GPL(__remove_pages);
 
-void online_page(struct page *page)
+int register_online_page_callback(online_page_callback_t callback)
+{
+       int rc = -EPERM;
+
+       lock_memory_hotplug();
+
+       if (online_page_callback == generic_online_page) {
+               online_page_callback = callback;
+               rc = 0;
+       }
+
+       unlock_memory_hotplug();
+
+       return rc;
+}
+EXPORT_SYMBOL_GPL(register_online_page_callback);
+
+int unregister_online_page_callback(online_page_callback_t callback)
+{
+       int rc = -EPERM;
+
+       lock_memory_hotplug();
+
+       if (online_page_callback == callback) {
+               online_page_callback = generic_online_page;
+               rc = 0;
+       }
+
+       unlock_memory_hotplug();
+
+       return rc;
+}
+EXPORT_SYMBOL_GPL(unregister_online_page_callback);
+
+void __online_page_set_limits(struct page *page)
 {
        unsigned long pfn = page_to_pfn(page);
 
-       totalram_pages++;
        if (pfn >= num_physpages)
                num_physpages = pfn + 1;
+}
+EXPORT_SYMBOL_GPL(__online_page_set_limits);
+
+void __online_page_increment_counters(struct page *page)
+{
+       totalram_pages++;
 
 #ifdef CONFIG_HIGHMEM
        if (PageHighMem(page))
                totalhigh_pages++;
 #endif
+}
+EXPORT_SYMBOL_GPL(__online_page_increment_counters);
 
+void __online_page_free(struct page *page)
+{
        ClearPageReserved(page);
        init_page_count(page);
        __free_page(page);
 }
+EXPORT_SYMBOL_GPL(__online_page_free);
+
+static void generic_online_page(struct page *page)
+{
+       __online_page_set_limits(page);
+       __online_page_increment_counters(page);
+       __online_page_free(page);
+}
 
 static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
                        void *arg)
@@ -388,7 +450,7 @@ static int online_pages_range(unsigned long start_pfn, 
unsigned long nr_pages,
        if (PageReserved(pfn_to_page(start_pfn)))
                for (i = 0; i < nr_pages; i++) {
                        page = pfn_to_page(start_pfn + i);
-                       online_page(page);
+                       online_page_callback(page);
                        onlined_pages++;
                }
        *(unsigned long *)arg = onlined_pages;
-- 
1.5.6.5

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