[PATCH v3 06/11] mm/memory_hotplug: Allow arch_remove_pages() without CONFIG_MEMORY_HOTREMOVE

[Michal Hocko]

On Mon 01-07-19 10:01:41, Michal Hocko wrote:
> On Mon 27-05-19 13:11:47, David Hildenbrand wrote:
> > We want to improve error handling while adding memory by allowing
> > to use arch_remove_memory() and __remove_pages() even if
> > CONFIG_MEMORY_HOTREMOVE is not set to e.g., implement something like:
> > 
> > 	arch_add_memory()
> > 	rc = do_something();
> > 	if (rc) {
> > 		arch_remove_memory();
> > 	}
> > 
> > We won't get rid of CONFIG_MEMORY_HOTREMOVE for now, as it will require
> > quite some dependencies for memory offlining.
> 
> If we cannot really remove CONFIG_MEMORY_HOTREMOVE altogether then why
> not simply add an empty placeholder for arch_remove_memory when the
> config is disabled?

In other words, can we replace this by something as simple as:

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ae892eef8b82..0329027fe740 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -128,6 +128,20 @@ extern void arch_remove_memory(int nid, u64 start, u64 size,
 			       struct vmem_altmap *altmap);
 extern void __remove_pages(struct zone *zone, unsigned long start_pfn,
 			   unsigned long nr_pages, struct vmem_altmap *altmap);
+#else
+/*
+ * Allow code using
+ * arch_add_memory();
+ * rc = do_something();
+ * if (rc)
+ * 	arch_remove_memory();
+ *
+ * without ifdefery.
+ */
+static inline void arch_remove_memory(int nid, u64 start, u64 size,
+			       struct vmem_altmap *altmap)
+{
+}
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
 /*
-- 
Michal Hocko
SUSE Labs