On Tue, Feb 09, 2021 at 02:38:47PM +0100, Oscar Salvador wrote: > Hi, > > here is v2. > > Changes from v1 -> v2 > - Addressed feedback from David > - Fence off the feature in case struct page size is not > multiple of PMD size or pageblock alignment cannot be guaranted > - Tested on x86_64 small and large memory_blocks > - Tested on arm64 4KB and 64KB page sizes (for some reason I cannot boot > my VM with 16KB page size). > > Arm64 with 4KB page size behaves like x86_64 after [1], which made section > size smaller. > With 64KB, the feature gets fenced off due to pageblock alignment. > > Changes from RFCv3 -> v1: > - Addressed feedback from David > - Re-order patches > > Changes from v2 -> v3 (RFC): > - Re-order patches (Michal) > - Fold "mm,memory_hotplug: Introduce MHP_MEMMAP_ON_MEMORY" in patch#1 > - Add kernel boot option to enable this feature (Michal) > > Changes from v1 -> v2 (RFC): > - Addressed feedback provided by David > - Add a arch_support_memmap_on_memory to be called > from mhp_supports_memmap_on_memory, as atm, > only ARM, powerpc and x86_64 have altmat support. > > [1] https://lore.kernel.org/lkml/cover.1611206601.git.sudaraja@xxxxxxxxxxxxxx/ Let me refloat this one :-) > > Original cover letter: > > ---- > > The primary goal of this patchset is to reduce memory overhead of the > hot-added memory (at least for SPARSEMEM_VMEMMAP memory model). > The current way we use to populate memmap (struct page array) has two main drawbacks: > > a) it consumes an additional memory until the hotadded memory itself is > onlined and > b) memmap might end up on a different numa node which is especially true > for movable_node configuration. > c) due to fragmentation we might end up populating memmap with base > pages > > One way to mitigate all these issues is to simply allocate memmap array > (which is the largest memory footprint of the physical memory hotplug) > from the hot-added memory itself. SPARSEMEM_VMEMMAP memory model allows > us to map any pfn range so the memory doesn't need to be online to be > usable for the array. See patch 3 for more details. > This feature is only usable when CONFIG_SPARSEMEM_VMEMMAP is set. > > [Overall design]: > > Implementation wise we reuse vmem_altmap infrastructure to override > the default allocator used by vmemap_populate. > memory_block structure gained a new field called nr_vmemmap_pages. > This plays well for two reasons: > > 1) {offline/online}_pages know the difference between start_pfn and > buddy_start_pfn, which is start_pfn + nr_vmemmap_pages. > In this way all isolation/migration operations are > done to within the right range of memory without vmemmap pages. > This allows us for a much cleaner handling. > > 2) In try_remove_memory, we construct a new vmemap_altmap struct with the > right information based on memory_block->nr_vmemap_pages, so we end up > calling vmem_altmap_free instead of free_pagetable when removing the memory. > > Oscar Salvador (7): > mm,memory_hotplug: Allocate memmap from the added memory range > acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported > mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory > mm,memory_hotplug: Enforce struct page size to be multiple of PMD > mm,memory_hotplug: Enforce pageblock alignment when memmap_on_memory > x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE > arm64/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE > > Documentation/admin-guide/kernel-parameters.txt | 14 +++ > arch/arm64/Kconfig | 4 + > arch/x86/Kconfig | 4 + > drivers/acpi/acpi_memhotplug.c | 5 +- > drivers/base/memory.c | 20 ++-- > include/linux/memory.h | 8 +- > include/linux/memory_hotplug.h | 21 +++- > include/linux/memremap.h | 2 +- > include/linux/mmzone.h | 5 + > mm/Kconfig | 3 + > mm/Makefile | 5 +- > mm/memory_hotplug.c | 150 ++++++++++++++++++++---- > mm/page_alloc.c | 4 +- > 13 files changed, 208 insertions(+), 37 deletions(-) > > -- > 2.16.3 > > -- Oscar Salvador SUSE L3
