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[195.135.221.5]) by mx.google.com with ESMTPS id s8si4367175pgl.503.2018.11.16.02.13.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Nov 2018 02:13:09 -0800 (PST) Received-SPF: pass (google.com: domain of osalvador@suse.com designates 195.135.221.5 as permitted sender) client-ip=195.135.221.5; Authentication-Results: mx.google.com; spf=pass (google.com: domain of osalvador@suse.com designates 195.135.221.5 as permitted sender) smtp.mailfrom=osalvador@suse.com Received: from emea4-mta.ukb.novell.com ([10.120.13.87]) by smtp.nue.novell.com with ESMTP (TLS encrypted); Fri, 16 Nov 2018 11:13:07 +0100 Received: from d104.suse.de (nwb-a10-snat.microfocus.com [10.120.13.202]) by emea4-mta.ukb.novell.com with ESMTP (NOT encrypted); Fri, 16 Nov 2018 10:12:50 +0000 From: Oscar Salvador To: linux-mm@kvack.org Cc: mhocko@suse.com, david@redhat.com, rppt@linux.vnet.ibm.com, akpm@linux-foundation.org, arunks@codeaurora.org, bhe@redhat.com, dan.j.williams@intel.com, Pavel.Tatashin@microsoft.com, Jonathan.Cameron@huawei.com, jglisse@redhat.com, linux-kernel@vger.kernel.org, Oscar Salvador Subject: [RFC PATCH 0/4] mm, memory_hotplug: allocate memmap from hotadded memory Date: Fri, 16 Nov 2018 11:12:18 +0100 Message-Id: <20181116101222.16581-1-osalvador@suse.com> X-Mailer: git-send-email 2.13.6 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Hi, this patchset is based on Michal's patchset [1]. Patch#1, patch#2 and patch#4 are quite the same. They just needed little changes to adapt it to current codestream, so it seemed fair to leave them. --------- Original cover: This is another step to make the memory hotplug more usable. The primary goal of this patchset is to reduce memory overhead of the hot added memory (at least for SPARSE_VMEMMAP memory model). Currently we use kmalloc to poppulate memmap (struct page array) which has two main drawbacks a) it consumes an additional memory until the hotadded memory itslef is onlined and b) memmap might end up on a different numa node which is especially true for movable_node configuration. a) is problem especially for memory hotplug based memory "ballooning" solutions when the delay between physical memory hotplug and the onlining can lead to OOM and that led to introduction of hacks like auto onlining (see 31bc3858ea3e ("memory-hotplug: add automatic onlining policy for the newly added memory")). b) can have performance drawbacks. One way to mitigate both issues is to simply allocate memmap array (which is the largest memory footprint of the physical memory hotplug) from the hotadded memory itself. 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. In short I am reusing an existing vmem_altmap which wants to achieve the same thing for nvdim device memory. There is also one potential drawback, though. If somebody uses memory hotplug for 1G (gigantic) hugetlb pages then this scheme will not work for them obviously because each memory block will contain reserved area. Large x86 machines will use 2G memblocks so at least one 1G page will be available but this is still not 2G... I am not really sure somebody does that and how reliable that can work actually. Nevertheless, I _believe_ that onlining more memory into virtual machines is much more common usecase. Anyway if there ever is a strong demand for such a usecase we have basically 3 options a) enlarge memory blocks even more b) enhance altmap allocation strategy and reuse low memory sections to host memmaps of other sections on the same NUMA node c) have the memmap allocation strategy configurable to fallback to the current allocation. --------- Old version of this patchset would blow up because we were clearing the pmds while we still had to reference pages backed by that memory. I picked another approach which does not force us to touch arch specific code in that regard. Overall design: With the preface of: 1) Whenever you hot-add a range, this is the same range that will be hot-removed. This is just because you can't remove half of a DIMM, in the same way you can't remove half of a device in qemu. A device/DIMM are added/removed as a whole. 2) Every add_memory()->add_memory_resource()->arch_add_memory()->__add_pages() will use a new altmap because it is a different hot-added range. 3) When you hot-remove a range, the sections will be removed sequantially starting from the first section of the range and ending with the last one. 4) hot-remove operations are protected by hotplug lock, so no parallel operations can take place. The current design is as follows: hot-remove operation) - __kfree_section_memmap will be called for every section to be removed. - We catch the first vmemmap_page and we pin it to a global variable. - Further calls to __kfree_section_memmap will decrease refcount of the vmemmap page without calling vmemmap_free(). We defer the call to vmemmap_free() untill all sections are removed - If the refcount drops to 0, we know that we hit the last section. - We clear the global variable. - We call vmemmap_free for [last_section, current_vmemmap_page) In case we are hot-removing a range that used altmap, the call to vmemmap_free must be done backwards, because the beginning of memory is used for the pagetables. Doing it this way, we ensure that by the time we remove the pagetables, those pages will not have to be referenced anymore. An example: (qemu) object_add memory-backend-ram,id=ram0,size=10G (qemu) device_add pc-dimm,id=dimm0,memdev=ram0,node=1 - This has added: ffffea0004000000 - ffffea000427ffc0 (refcount: 80) When refcount of ffffea0004000000 drops to 0, vmemmap_free() will be called in this way: vmemmap_free: start/end: ffffea000de00000 - ffffea000e000000 vmemmap_free: start/end: ffffea000dc00000 - ffffea000de00000 vmemmap_free: start/end: ffffea000da00000 - ffffea000dc00000 vmemmap_free: start/end: ffffea000d800000 - ffffea000da00000 vmemmap_free: start/end: ffffea000d600000 - ffffea000d800000 vmemmap_free: start/end: ffffea000d400000 - ffffea000d600000 vmemmap_free: start/end: ffffea000d200000 - ffffea000d400000 vmemmap_free: start/end: ffffea000d000000 - ffffea000d200000 vmemmap_free: start/end: ffffea000ce00000 - ffffea000d000000 vmemmap_free: start/end: ffffea000cc00000 - ffffea000ce00000 vmemmap_free: start/end: ffffea000ca00000 - ffffea000cc00000 vmemmap_free: start/end: ffffea000c800000 - ffffea000ca00000 vmemmap_free: start/end: ffffea000c600000 - ffffea000c800000 vmemmap_free: start/end: ffffea000c400000 - ffffea000c600000 vmemmap_free: start/end: ffffea000c200000 - ffffea000c400000 vmemmap_free: start/end: ffffea000c000000 - ffffea000c200000 vmemmap_free: start/end: ffffea000be00000 - ffffea000c000000 ... ... vmemmap_free: start/end: ffffea0004000000 - ffffea0004200000 [Testing] - Tested ony on x86_64 - Several tests were carried out with memblocks of different sizes. - Tests were performed adding different memory-range sizes from 512M to 60GB. [Todo] - Look into hotplug gigantic pages case Before investing more effort, I would like to hear some opinions/thoughts/ideas. [1] https://lore.kernel.org/lkml/20170801124111.28881-1-mhocko@kernel.org/ Michal Hocko (3): mm, memory_hotplug: cleanup memory offline path mm, memory_hotplug: provide a more generic restrictions for memory hotplug mm, sparse: rename kmalloc_section_memmap, __kfree_section_memmap Oscar Salvador (1): mm, memory_hotplug: allocate memmap from the added memory range for sparse-vmemmap arch/arm64/mm/mmu.c | 5 +- arch/ia64/mm/init.c | 5 +- arch/powerpc/mm/init_64.c | 2 + arch/powerpc/mm/mem.c | 6 +- arch/s390/mm/init.c | 12 +++- arch/sh/mm/init.c | 6 +- arch/x86/mm/init_32.c | 6 +- arch/x86/mm/init_64.c | 17 ++++-- include/linux/memory_hotplug.h | 35 ++++++++--- include/linux/memremap.h | 65 +++++++++++++++++++- include/linux/page-flags.h | 18 ++++++ kernel/memremap.c | 12 ++-- mm/compaction.c | 3 + mm/hmm.c | 6 +- mm/memory_hotplug.c | 133 ++++++++++++++++++++++++++++------------- mm/page_alloc.c | 33 ++++++++-- mm/page_isolation.c | 13 +++- mm/sparse.c | 62 ++++++++++++++++--- 18 files changed, 345 insertions(+), 94 deletions(-)