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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-460d3c62f4dsm33845841cf.28.2024.10.22.14.34.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Oct 2024 14:34:49 -0700 (PDT) From: Gregory Price To: x86@kernel.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-mm@kvack.org Cc: linux-cxl@kvack.org, Jonathan.Cameron@huawei.com, dan.j.williams@intel.com, rrichter@amd.com, Terry.Bowman@amd.com, dave.jiang@intel.com, ira.weiny@intel.com, alison.schofield@intel.com, gourry@gourry.net, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, rafael@kernel.org, lenb@kernel.org, david@redhat.com, osalvador@suse.de, gregkh@linuxfoundation.org, akpm@linux-foundation.org, rppt@kernel.org Subject: [PATCH v3 0/3] memory,x86,acpi: hotplug memory alignment advisement Date: Tue, 22 Oct 2024 17:34:47 -0400 Message-ID: <20241022213450.15041-1-gourry@gourry.net> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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/probe functions in driverse/base/memory.c to report/probe architecture agnostic hotplug memory 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 probe() 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. Suggested-by: Ira Weiny Suggested-by: David Hildenbrand Suggested-by: Dan Williams Signed-off-by: Gregory Price 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 | 14 ++++++++----- drivers/acpi/numa/srat.c | 33 ++++++++++++++++++++++++++++++ drivers/base/memory.c | 43 ++++++++++++++++++++++++++++++++++++++++ include/linux/memory.h | 10 ++++++++++ 4 files changed, 95 insertions(+), 5 deletions(-)