Messages in this thread | | | Date | Mon, 27 Nov 2023 16:50:59 +0100 | Subject | Re: [PATCH v3 1/5] mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers | From | David Hildenbrand <> |
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On 27.11.23 09:20, Sumanth Korikkar wrote: > Introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers to > prepare the transition of memory to and from a physically accessible > state. This enhancement is crucial for implementing the "memmap on > memory" feature for s390 in a subsequent patch. > > Platforms such as x86 can support physical memory hotplug via ACPI. When > there is physical memory hotplug, ACPI event leads to the memory > addition with the following callchain: > acpi_memory_device_add() > -> acpi_memory_enable_device() > -> __add_memory() > > After this, the hotplugged memory is physically accessible, and altmap > support prepared, before the "memmap on memory" initialization in > memory_block_online() is called. > > On s390, memory hotplug works in a different way. The available hotplug > memory has to be defined upfront in the hypervisor, but it is made > physically accessible only when the user sets it online via sysfs, > currently in the MEM_GOING_ONLINE notifier. This is too late and "memmap > on memory" initialization is performed before calling MEM_GOING_ONLINE > notifier. > > During the memory hotplug addition phase, altmap support is prepared and > during the memory onlining phase s390 requires memory to be physically > accessible and then subsequently initiate the "memmap on memory" > initialization process. > > The memory provider will handle new MEM_PREPARE_ONLINE / > MEM_FINISH_OFFLINE notifications and make the memory accessible. > > The mhp_flag MHP_OFFLINE_INACCESSIBLE is introduced and is relevant when > used along with MHP_MEMMAP_ON_MEMORY, because the altmap cannot be > written (e.g., poisoned) when adding memory -- before it is set online. > This allows for adding memory with an altmap that is not currently made > available by a hypervisor. When onlining that memory, the hypervisor can > be instructed to make that memory accessible via the new notifiers and > the onlining phase will not require any memory allocations, which is > helpful in low-memory situations. > > All architectures ignore unknown memory notifiers. Therefore, the > introduction of these new notifiers does not result in any functional > modifications across architectures. > > Suggested-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> > Suggested-by: David Hildenbrand <david@redhat.com> > Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com> > --- > drivers/base/memory.c | 21 +++++++++++++++++++-- > include/linux/memory.h | 2 ++ > include/linux/memory_hotplug.h | 18 +++++++++++++++++- > include/linux/memremap.h | 1 + > mm/memory_hotplug.c | 30 ++++++++++++++++++++++++++++-- > mm/sparse.c | 3 ++- > 6 files changed, 69 insertions(+), 6 deletions(-) > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c > index 8a13babd826c..5c6b2af75db4 100644 > --- a/drivers/base/memory.c > +++ b/drivers/base/memory.c > @@ -188,6 +188,7 @@ static int memory_block_online(struct memory_block *mem) > unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr); > unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block; > unsigned long nr_vmemmap_pages = 0; > + struct memory_notify arg; > struct zone *zone; > int ret; > > @@ -197,6 +198,14 @@ static int memory_block_online(struct memory_block *mem) > zone = zone_for_pfn_range(mem->online_type, mem->nid, mem->group, > start_pfn, nr_pages); > > + arg.start_pfn = start_pfn; > + arg.nr_pages = nr_pages;
Thinking about it, it's possibly cleanest to send the altmap range along here.
Later memory onlining notifiers will only be notified about the actual !altmap part.
arg.altmap_start_pfn = start_pfn; arg.altmap_nr_pages = nr_vmemmap_pages; arg.start_pfn = start_pfn + nr_vmemmap_pages; arg.nr_pages = nr_pages - nr_vmemmap_pages;
Use that for the two new notifiers only and document it. Thoughts?
-- Cheers,
David / dhildenb
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