Re: [PATCH v2 4/8] mm/memory_hotplug: Create memory block devices after arch_add_memory()

[Wei Yang]

On Tue, May 07, 2019 at 08:38:00PM +0200, David Hildenbrand wrote:
>Only memory to be added to the buddy and to be onlined/offlined by
>user space using memory block devices needs (and should have!) memory
>block devices.
>
>Factor out creation of memory block devices Create all devices after
>arch_add_memory() succeeded. We can later drop the want_memblock parameter,
>because it is now effectively stale.
>
>Only after memory block devices have been added, memory can be onlined
>by user space. This implies, that memory is not visible to user space at
>all before arch_add_memory() succeeded.
>
>Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
>Cc: David Hildenbrand <david@xxxxxxxxxx>
>Cc: "mike.travis@xxxxxxx" <mike.travis@xxxxxxx>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>Cc: Andrew Banman <andrew.banman@xxxxxxx>
>Cc: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Michal Hocko <mhocko@xxxxxxxx>
>Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
>Cc: Qian Cai <cai@xxxxxx>
>Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
>Cc: Arun KS <arunks@xxxxxxxxxxxxxx>
>Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>---
> drivers/base/memory.c  | 70 ++++++++++++++++++++++++++----------------
> include/linux/memory.h |  2 +-
> mm/memory_hotplug.c    | 15 ++++-----
> 3 files changed, 53 insertions(+), 34 deletions(-)
>
>diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>index 6e0cb4fda179..862c202a18ca 100644
>--- a/drivers/base/memory.c
>+++ b/drivers/base/memory.c
>@@ -701,44 +701,62 @@ static int add_memory_block(int base_section_nr)
> 	return 0;
> }
> 
>+static void unregister_memory(struct memory_block *memory)
>+{
>+	BUG_ON(memory->dev.bus != &memory_subsys);
>+
>+	/* drop the ref. we got via find_memory_block() */
>+	put_device(&memory->dev);
>+	device_unregister(&memory->dev);
>+}
>+
> /*
>- * need an interface for the VM to add new memory regions,
>- * but without onlining it.
>+ * Create memory block devices for the given memory area. Start and size
>+ * have to be aligned to memory block granularity. Memory block devices
>+ * will be initialized as offline.
>  */
>-int hotplug_memory_register(int nid, struct mem_section *section)
>+int hotplug_memory_register(unsigned long start, unsigned long size)
> {
>-	int ret = 0;
>+	unsigned long block_nr_pages = memory_block_size_bytes() >> PAGE_SHIFT;
>+	unsigned long start_pfn = PFN_DOWN(start);
>+	unsigned long end_pfn = start_pfn + (size >> PAGE_SHIFT);
>+	unsigned long pfn;
> 	struct memory_block *mem;
>+	int ret = 0;
> 
>-	mutex_lock(&mem_sysfs_mutex);
>+	BUG_ON(!IS_ALIGNED(start, memory_block_size_bytes()));
>+	BUG_ON(!IS_ALIGNED(size, memory_block_size_bytes()));
> 
>-	mem = find_memory_block(section);
>-	if (mem) {
>-		mem->section_count++;
>-		put_device(&mem->dev);
>-	} else {
>-		ret = init_memory_block(&mem, section, MEM_OFFLINE);
>+	mutex_lock(&mem_sysfs_mutex);
>+	for (pfn = start_pfn; pfn != end_pfn; pfn += block_nr_pages) {
>+		mem = find_memory_block(__pfn_to_section(pfn));
>+		if (mem) {
>+			WARN_ON_ONCE(false);

One question here, the purpose of WARN_ON_ONCE(false) is? Would we trigger
this?

>+			put_device(&mem->dev);
>+			continue;
>+		}
>+		ret = init_memory_block(&mem, __pfn_to_section(pfn),
>+					MEM_OFFLINE);
> 		if (ret)
>-			goto out;
>-		mem->section_count++;
>+			break;
>+		mem->section_count = memory_block_size_bytes() /
>+				     MIN_MEMORY_BLOCK_SIZE;

Maybe we can leverage sections_per_block variable.

                mem->section_count = sections_per_block;

>+	}
>+	if (ret) {
>+		end_pfn = pfn;
>+		for (pfn = start_pfn; pfn != end_pfn; pfn += block_nr_pages) {
>+			mem = find_memory_block(__pfn_to_section(pfn));
>+			if (!mem)
>+				continue;
>+			mem->section_count = 0;
>+			unregister_memory(mem);
>+		}
> 	}

-- 
Wei Yang
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