On 30.10.24 15:59, Gregory Price wrote:
On Wed, Oct 30, 2024 at 11:25:33AM +0100, David Hildenbrand wrote:
On 29.10.24 21:20, 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@xxxxxxxxx>
Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
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;
Nit: if everything is called "size", call this "size" as well.
Mostly shortened here because
if (memory_block_advised_sz)
memory_block_advised_size = min(size, memory_block_advised_size);
is over 80 characters lol. Happy to change if you have strong feelings.
Feel free to exceed 80 chars if there is good reason to -- like in this
case. checkpatch.pl nowadays complains if you exceed 100 chars.
No strong feelings, making it consistent in some way would be "nice" ;)
--
Cheers,
David / dhildenb
