Commit dff03381 authored by Muchun Song's avatar Muchun Song Committed by Andrew Morton
Browse files

mm: hugetlb_vmemmap: introduce the name HVO 

It it inconvenient to mention the feature of optimizing vmemmap pages
associated with HugeTLB pages when communicating with others since there
is no specific or abbreviated name for it when it is first introduced. 
Let us give it a name HVO (HugeTLB Vmemmap Optimization) from now.

This commit also updates the document about "hugetlb_free_vmemmap" by the
way discussed in thread [1].

Link: https://lore.kernel.org/all/21aae898-d54d-cc4b-a11f-1bb7fddcfffa@redhat.com/ [1]
Link: https://lkml.kernel.org/r/20220628092235.91270-4-songmuchun@bytedance.com


Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Will Deacon <will@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent cf5472e5

Documentation/admin-guide/kernel-parameters.txt

+4 −3
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@@ -1731,12 +1731,13 @@ 
	hugetlb_free_vmemmap=

			[KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

			enabled.

			Control if HugeTLB Vmemmap Optimization (HVO) is enabled.

			Allows heavy hugetlb users to free up some more

			memory (7 * PAGE_SIZE for each 2MB hugetlb page).

			Format: { [oO][Nn]/Y/y/1 | [oO][Ff]/N/n/0 (default) }

			Format: { on | off (default) }



			[oO][Nn]/Y/y/1: enable the feature

			[oO][Ff]/N/n/0: disable the feature

			on: enable HVO

			off: disable HVO



			Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,

			the default is on.

Documentation/admin-guide/mm/hugetlbpage.rst

+2 −2
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@@ -164,8 +164,8 @@ default_hugepagesz 
	will all result in 256 2M huge pages being allocated.  Valid default

	huge page size is architecture dependent.

hugetlb_free_vmemmap

	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables optimizing

	unused vmemmap pages associated with each HugeTLB page.

	When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables HugeTLB

	Vmemmap Optimization (HVO).



When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``

indicates the current number of pre-allocated huge pages of the default size.

Documentation/admin-guide/mm/memory-hotplug.rst

+2 −2
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@@ -653,8 +653,8 @@ block might fail: 
- Concurrent activity that operates on the same physical memory area, such as

  allocating gigantic pages, can result in temporary offlining failures.



- Out of memory when dissolving huge pages, especially when freeing unused

  vmemmap pages associated with each hugetlb page is enabled.

- Out of memory when dissolving huge pages, especially when HugeTLB Vmemmap

  Optimization (HVO) is enabled.



  Offlining code may be able to migrate huge page contents, but may not be able

  to dissolve the source huge page because it fails allocating (unmovable) pages

Documentation/admin-guide/sysctl/vm.rst

+1 −2
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@@ -569,8 +569,7 @@ This knob is not available when the size of 'struct page' (a structure defined 
in include/linux/mm_types.h) is not power of two (an unusual system config could

result in this).



Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages

associated with each HugeTLB page.

Enable (set to 1) or disable (set to 0) HugeTLB Vmemmap Optimization (HVO).



Once enabled, the vmemmap pages of subsequent allocation of HugeTLB pages from

buddy allocator will be optimized (7 pages per 2MB HugeTLB page and 4095 pages

Documentation/mm/vmemmap_dedup.rst

+2 −0
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@@ -7,6 +7,8 @@ A vmemmap diet for HugeTLB and Device DAX 
HugeTLB

=======



This section is to explain how HugeTLB Vmemmap Optimization (HVO) works.



The struct page structures (page structs) are used to describe a physical

page frame. By default, there is a one-to-one mapping from a page frame to

it's corresponding page struct.