On Wed, Nov 06, 2024 at 10:58:44AM -0500, Gregory Price wrote: > 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 (i.e. not 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 query has already > occurred, but this is predicated on the notion that query actually > occurs (which presently only happens on the x86 arch). This is to > assist debugging future users. Otherwise, the advise() call has > been marked __init to help static discovery of bad call times. > > Once query is called the first time, it will always return the same value. > > Interfaces return -EBUSY and 0 respectively on systems without hotplug. > > v6: > - boot_cpu_has -> cpu_feature_enabled() in x86 code > - ack tags > > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx> > Signed-off-by: Gregory Price <gourry@xxxxxxxxxx> > Tested on a CXL server with a directly attached cxl device, works as expected. Tested-by: Fan Ni <fan.ni@xxxxxxxxxxx> Fan > 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 | 15 ++++++++---- > drivers/acpi/numa/srat.c | 12 ++++++++- > drivers/base/memory.c | 53 ++++++++++++++++++++++++++++++++++++++++ > include/linux/memory.h | 10 ++++++++ > 4 files changed, 84 insertions(+), 6 deletions(-) > > -- > 2.43.0 > -- Fan Ni (From gmail)
