In order to keep pfn_to_page() a simple offset calculation the 'struct page' memmap needs to be mapped and initialized in advance of any usage of a page. This poses a problem for large memory systems as it delays full availability of memory resources for 10s to 100s of seconds. For typical 'System RAM' the problem is mitigated by the fact that large memory allocations tend to happen after the kernel has fully initialized and userspace services / applications are launched. A small amount, 2GB of memory, is initialized up front. The remainder is initialized in the background and freed to the page allocator over time. Unfortunately, that scheme is not directly reusable for persistent memory and dax because userspace has visibility to the entire resource pool and can choose to access any offset directly at its choosing. In other words there is no allocator indirection where the kernel can satisfy requests with arbitrary pages as they become initialized. That said, we can approximate the optimization by performing the initialization in the background, allow the kernel to fully boot the platform, start up pmem block devices, mount filesystems in dax mode, and only incur the delay at the first userspace dax fault. With this change an 8 socket system was observed to initialize pmem namespaces in ~4 seconds whereas it was previously taking ~4 minutes. These patches apply on top of the HMM + devm_memremap_pages() reworks [1]. Andrew, once the reviews come back, please consider this series for -mm as well. [1]: https://lkml.org/lkml/2018/6/19/108 --- Dan Williams (9): mm: Plumb dev_pagemap instead of vmem_altmap to memmap_init_zone() mm: Enable asynchronous __add_pages() and vmemmap_populate_hugepages() mm: Teach memmap_init_zone() to initialize ZONE_DEVICE pages mm: Multithread ZONE_DEVICE initialization mm: Allow an external agent to wait for memmap initialization filesystem-dax: Make mount time pfn validation a debug check libnvdimm, pmem: Initialize the memmap in the background device-dax: Initialize the memmap in the background libnvdimm, namespace: Publish page structure init state / control Huaisheng Ye (4): nvdimm/pmem: check the validity of the pointer pfn nvdimm/pmem-dax: check the validity of the pointer pfn s390/block/dcssblk: check the validity of the pointer pfn fs/dax: Assign NULL to pfn of dax_direct_access if useless arch/ia64/mm/init.c | 5 + arch/powerpc/mm/mem.c | 5 + arch/s390/mm/init.c | 8 + arch/sh/mm/init.c | 5 + arch/x86/mm/init_32.c | 8 + arch/x86/mm/init_64.c | 27 +++-- drivers/dax/Kconfig | 10 ++ drivers/dax/dax-private.h | 2 drivers/dax/device-dax.h | 2 drivers/dax/device.c | 16 +++ drivers/dax/pmem.c | 5 + drivers/dax/super.c | 64 +++++++----- drivers/nvdimm/nd.h | 2 drivers/nvdimm/pfn_devs.c | 54 ++++++++-- drivers/nvdimm/pmem.c | 17 ++- drivers/nvdimm/pmem.h | 1 drivers/s390/block/dcssblk.c | 5 + fs/dax.c | 10 +- include/linux/memmap_async.h | 55 ++++++++++ include/linux/memory_hotplug.h | 18 ++- include/linux/memremap.h | 31 ++++++ include/linux/mm.h | 8 + kernel/memremap.c | 85 ++++++++------- mm/memory_hotplug.c | 73 ++++++++++--- mm/page_alloc.c | 215 +++++++++++++++++++++++++++++++++------ mm/sparse-vmemmap.c | 56 ++++++++-- tools/testing/nvdimm/pmem-dax.c | 11 ++ 27 files changed, 610 insertions(+), 188 deletions(-) create mode 100644 include/linux/memmap_async.h
