| Message ID | 20241029202041.25334-1-gourry@gourry.net |
|---|---|
| Headers | show |
| Series | memory,x86,acpi: hotplug memory alignment advisement | expand |
On Tue, Oct 29, 2024 at 04:20:39PM -0400, Gregory Price wrote: > Hotplug memory sources may have opinions on what the memblock size > should be - usually for alignment purposes. For example, CXL memory > extents can be 256MB with a matching alignment. If this size/alignment > is smaller than the block size, it can result in stranded capacity. > > Implement memory_block_advise_max_size for use prior to allocator init, > for software to advise the system on the max block size. > > Implement memory_block_probe_max_size for use by arch init code to > calculate the best block size. Use of advice is architecture defined. > > The probe value can never change after first probe. Calls to advise > after probe will return -EBUSY to aid debugging. > > On systems without hotplug, always return -ENODEV and 0 respectively. > > Suggested-by: Ira Weiny <ira.weiny@intel.com> > Signed-off-by: Gregory Price <gourry@gourry.net> > --- > drivers/base/memory.c | 48 ++++++++++++++++++++++++++++++++++++++++++ > include/linux/memory.h | 10 +++++++++ > 2 files changed, 58 insertions(+) > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c > index 67858eeb92ed..099a972c52dc 100644 > --- a/drivers/base/memory.c > +++ b/drivers/base/memory.c > @@ -110,6 +110,54 @@ static void memory_block_release(struct device *dev) > kfree(mem); > } > > +/** > + * memory_block_advise_max_size() - advise memory hotplug on the max suggested > + * block size, usually for alignment. > + * @size: suggestion for maximum block size. must be aligned on power of 2. > + * > + * Early boot software (pre-allocator init) may advise archs on the max block > + * size. This value can only decrease after initialization, as the intent is > + * to identify the largest supported alignment for all sources. > + * > + * Use of this value is arch-defined, as is min/max block size. > + * > + * Return: 0 on success > + * -EINVAL if size is 0 or not pow2 aligned > + * -EBUSY if value has already been probed > + */ > +static size_t memory_block_advised_sz; > +static bool memory_block_advised_size_queried; kernel-doc will be unhappy about variable declarations between the doc block and the function it describes > +int memory_block_advise_max_size(size_t size) > +{ > + if (!size || !is_power_of_2(size)) > + return -EINVAL; > + > + if (memory_block_advised_size_queried) > + return -EBUSY; > + > + if (memory_block_advised_sz) > + memory_block_advised_sz = min(size, memory_block_advised_sz); > + else > + memory_block_advised_sz = size; > + > + return 0; > +} > + > +/** > + * memory_block_advised_max_size() - query advised max hotplug block size. > + * > + * After the first call, the value can never change. Callers looking for the > + * actual block size should use memory_block_size_bytes. This interface is > + * intended for use by arch-init when initializing the hotplug block size. > + * > + * Return: advised size in bytes, or 0 if never set. > + */ > +size_t memory_block_advised_max_size(void) > +{ > + memory_block_advised_size_queried = true; > + return memory_block_advised_sz; > +} > + > unsigned long __weak memory_block_size_bytes(void) > { > return MIN_MEMORY_BLOCK_SIZE; > diff --git a/include/linux/memory.h b/include/linux/memory.h > index c0afee5d126e..07e20a77b717 100644 > --- a/include/linux/memory.h > +++ b/include/linux/memory.h > @@ -149,6 +149,14 @@ static inline int hotplug_memory_notifier(notifier_fn_t fn, int pri) > { > return 0; > } > +static inline int memory_block_advise_max_size(size_t size) > +{ > + return -ENODEV; > +} > +static inline size_t memory_block_advised_max_size(void) > +{ > + return 0; > +} > #else /* CONFIG_MEMORY_HOTPLUG */ > extern int register_memory_notifier(struct notifier_block *nb); > extern void unregister_memory_notifier(struct notifier_block *nb); > @@ -181,6 +189,8 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func, > void memory_block_add_nid(struct memory_block *mem, int nid, > enum meminit_context context); > #endif /* CONFIG_NUMA */ > +int memory_block_advise_max_size(size_t size); > +size_t memory_block_advised_max_size(void); > #endif /* CONFIG_MEMORY_HOTPLUG */ > > /* > -- > 2.43.0 >
When physical address regions are not aligned to memory block size, the misaligned portion is lost (stranded capacity). Block size (min/max/selected) is architecture defined. Most architectures tend to use the minimum block size or some simplistic heurist. On x86, memory block size increases up to 2GB, and is otherwise fitted to the alignment of non-hotplug (special purpose memory). CXL exposes its memory for management through the ACPI CEDT (CXL Early Detection Table) in a field called the CXL Fixed Memory Window. Per the CXL specification, this memory must be aligned to at least 256MB. When a CFMW aligns on a size less than the block size, this causes a loss of up to 2GB per CFMW on x86. It is not uncommon for CFMW to be allocated per-device - though this behavior is BIOS defined. This patch set provides 3 things: 1) implement advise/query functions in driverse/base/memory.c to report/query architecture agnostic hotplug block alignment advice. 2) update x86 memblock size logic to consider the hotplug advice 3) add code in acpi/numa/srat.c to report CFMW alignment advice The advisement interfaces are design to be called during arch_init code prior to allocator and smp_init. start_kernel will call these through setup_arch() (via acpi and mm/init_64.c on x86), which occurs prior to mm_core_init and smp_init - so no need for atomics. There's an attempt to signal callers to advise() that probe has already occurred, but this is predicated on the notion that query actually occurs (which presently only happens on x86 and acpi logic). This is to assist debugging future users. Once probe is called the first time, it will always return the same value. Interfaces return -EBUSY and 0 respectively on systems without hotplug. v4: - nits and renames - consolidate srat logic into existing iterator - remove lock-in call from srat code Suggested-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: David Hildenbrand <david@redhat.com> Suggested-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Gregory Price <gourry@gourry.net> Gregory Price (3): memory: implement memory_block_advise/probe_max_size x86: probe memory block size advisement value during mm init acpi,srat: give memory block size advice based on CFMWS alignment arch/x86/mm/init_64.c | 16 +++++++++----- drivers/acpi/numa/srat.c | 19 ++++++++++++++-- drivers/base/memory.c | 48 ++++++++++++++++++++++++++++++++++++++++ include/linux/memory.h | 10 +++++++++ 4 files changed, 85 insertions(+), 8 deletions(-)