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

From: Wei Yang <[email-masked]>
Date: Thu, 9 May 2019 12:43:02 +0000

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 <[email-masked]>
>Cc: "Rafael J. Wysocki" <[email-masked]>
>Cc: David Hildenbrand <[email-masked]>
>Cc: "[email-masked]" <[email-masked]>
>Cc: Andrew Morton <[email-masked]>
>Cc: Ingo Molnar <[email-masked]>
>Cc: Andrew Banman <[email-masked]>
>Cc: Oscar Salvador <[email-masked]>
>Cc: Michal Hocko <[email-masked]>
>Cc: Pavel Tatashin <[email-masked]>
>Cc: Qian Cai <[email-masked]>
>Cc: Wei Yang <[email-masked]>
>Cc: Arun KS <[email-masked]>
>Cc: Mathieu Malaterre <[email-masked]>
>Signed-off-by: David Hildenbrand <[email-masked]>
>---
> 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()));

After this change, the call flow looks like this:

add_memory_resource
    check_hotplug_memory_range
    hotplug_memory_register

Since in check_hotplug_memory_range() has checked the boundary, do we need to
check here again?

-- 
Wei Yang
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