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Message-ID: <1e15544f-ba35-4be6-b77a-f3e1daafe24a@redhat.com>
Date: Tue, 28 Nov 2023 12:08:58 +0100
From: David Hildenbrand <david@...hat.com>
To: Sumanth Korikkar <sumanthk@...ux.ibm.com>,
linux-mm <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
linux-s390 <linux-s390@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/5] mm/memory_hotplug: introduce
MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers
On 28.11.23 12:03, 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@...ux.ibm.com>
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
> drivers/base/memory.c | 23 ++++++++++++++++++++++-
> include/linux/memory.h | 9 +++++++++
> include/linux/memory_hotplug.h | 18 +++++++++++++++++-
> include/linux/memremap.h | 1 +
> mm/memory_hotplug.c | 13 ++++++++++++-
> mm/sparse.c | 3 ++-
> 6 files changed, 63 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 8a13babd826c..b99bcc70d6e5 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;
>
> @@ -207,9 +208,19 @@ static int memory_block_online(struct memory_block *mem)
> if (mem->altmap)
> nr_vmemmap_pages = mem->altmap->free;
>
> + 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;
> mem_hotplug_begin();
> + ret = memory_notify(MEM_PREPARE_ONLINE, &arg);
> + ret = notifier_to_errno(ret);
> + if (ret)
> + goto out_notifier;
> +
> if (nr_vmemmap_pages) {
> - ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone);
> + ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages,
> + zone, mem->altmap->inaccessible);
> if (ret)
> goto out;
> }
> @@ -231,7 +242,11 @@ static int memory_block_online(struct memory_block *mem)
> nr_vmemmap_pages);
>
> mem->zone = zone;
> + mem_hotplug_done();
> + return ret;
> out:
> + memory_notify(MEM_FINISH_OFFLINE, &arg);
> +out_notifier:
> mem_hotplug_done();
> return ret;
> }
> @@ -244,6 +259,7 @@ static int memory_block_offline(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;
> int ret;
>
> if (!mem->zone)
> @@ -275,6 +291,11 @@ static int memory_block_offline(struct memory_block *mem)
> mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
>
> mem->zone = NULL;
> + 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;
> + memory_notify(MEM_FINISH_OFFLINE, &arg);
> out:
> mem_hotplug_done();
> return ret;
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index f53cfdaaaa41..939a16bd5cea 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -96,8 +96,17 @@ int set_memory_block_size_order(unsigned int order);
> #define MEM_GOING_ONLINE (1<<3)
> #define MEM_CANCEL_ONLINE (1<<4)
> #define MEM_CANCEL_OFFLINE (1<<5)
> +#define MEM_PREPARE_ONLINE (1<<6)
> +#define MEM_FINISH_OFFLINE (1<<7)
>
> struct memory_notify {
> + /*
> + * The altmap_start_pfn and altmap_nr_pages fields are designated for
> + * specifying the altmap range and are exclusively intended for use in
> + * MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers.
> + */
> + unsigned long altmap_start_pfn;
> + unsigned long altmap_nr_pages;
> unsigned long start_pfn;
> unsigned long nr_pages;
> int status_change_nid_normal;
Maybe we should do something like:
union {
/* For MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE ... */
struct {
unsigned long altmap_start_pfn;
unnsigned long altmap_nr_pages;
};
/* For all others ... */
struct {
int status_change_nid_normal;
...
};
}
Acked-by: David Hildenbrand <david@...hat.com>
--
Cheers,
David / dhildenb
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