| Message ID | 20241106155847.7985-2-gourry@gourry.net |
|---|---|
| State | New |
| Headers | show |
| Series | memory,x86,acpi: hotplug memory alignment advisement | expand |
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. Should the advice just succeed when the result does not matter? Otherwise, it depends on the caller to not care based on config. I do not feel that strongly about it, so either way: Acked-by: Dan Williams <dan.j.williams@intel.com>
On Tue, Nov 12, 2024 at 01:28:03PM -0800, Dan Williams wrote: > 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. > > Should the advice just succeed when the result does not matter? > I figure at some point during __init the value will be probed and subsequent calls will be ignored. I'd rather fail explicitly in that case to assist debugging - otherwise it might be a little maddening to discover your callsite is too late in the process. > Otherwise, it depends on the caller to not care based on config. > > I do not feel that strongly about it, so either way: > > Acked-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/base/memory.c b/drivers/base/memory.c index 67858eeb92ed..835793150b41 100644 --- a/drivers/base/memory.c +++ b/drivers/base/memory.c @@ -110,6 +110,59 @@ static void memory_block_release(struct device *dev) kfree(mem); } + +/* Max block size to be set by memory_block_advise_max_size */ +static unsigned long memory_block_advised_size; +static bool memory_block_advised_size_queried; + +/** + * 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 + */ +int __init memory_block_advise_max_size(unsigned long size) +{ + if (!size || !is_power_of_2(size)) + return -EINVAL; + + if (memory_block_advised_size_queried) + return -EBUSY; + + if (memory_block_advised_size) { + memory_block_advised_size = min(memory_block_advised_size, + size); + } else { + memory_block_advised_size = 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. + */ +unsigned long memory_block_advised_max_size(void) +{ + memory_block_advised_size_queried = true; + return memory_block_advised_size; +} + 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..8202d0efbf46 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(unsigned long size) +{ + return -ENODEV; +} +static inline unsigned long 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(unsigned long size); +unsigned long memory_block_advised_max_size(void); #endif /* CONFIG_MEMORY_HOTPLUG */ /*