Commit 66361095 authored by Muchun Song's avatar Muchun Song Committed by Andrew Morton
Browse files

mm: memory_hotplug: make hugetlb_optimize_vmemmap compatible with memmap_on_memory 

For now, the feature of hugetlb_free_vmemmap is not compatible with the
feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap takes
precedence over memory_hotplug.memmap_on_memory.  However, someone wants
to make memory_hotplug.memmap_on_memory takes precedence over
hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
succeed memory hotplug in close-to-OOM situations.  So the decision of
making hugetlb_free_vmemmap take precedence is not wise and elegant.

The proper approach is to have hugetlb_vmemmap.c do the check whether the
section which the HugeTLB pages belong to can be optimized.  If the
section's vmemmap pages are allocated from the added memory block itself,
hugetlb_free_vmemmap should refuse to optimize the vmemmap, otherwise, do
the optimization.  Then both kernel parameters are compatible.  So this
patch introduces VmemmapSelfHosted to mask any non-optimizable vmemmap
pages.  The hugetlb_vmemmap can use this flag to detect if a vmemmap page
can be optimized.

[songmuchun@bytedance.com: walk vmemmap page tables to avoid false-positive]
  Link: https://lkml.kernel.org/r/20220620110616.12056-3-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20220617135650.74901-3-songmuchun@bytedance.com


Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Co-developed-by: default avatarOscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarOscar Salvador <osalvador@suse.de>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ed7802dd

Documentation/admin-guide/kernel-parameters.txt

+11 −11
Original line number Diff line number Diff line
@@ -1722,9 +1722,11 @@ 
			Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,

			the default is on.



			This is not compatible with memory_hotplug.memmap_on_memory.

			If both parameters are enabled, hugetlb_free_vmemmap takes

			precedence over memory_hotplug.memmap_on_memory.

			Note that the vmemmap pages may be allocated from the added

			memory block itself when memory_hotplug.memmap_on_memory is

			enabled, those vmemmap pages cannot be optimized even if this

			feature is enabled.  Other vmemmap pages not allocated from

			the added memory block itself do not be affected.



	hung_task_panic=

			[KNL] Should the hung task detector generate panics.
@@ -3068,10 +3070,12 @@ 
			[KNL,X86,ARM] Boolean flag to enable this feature.

			Format: {on | off (default)}

			When enabled, runtime hotplugged memory will

			allocate its internal metadata (struct pages)

			from the hotadded memory which will allow to

			hotadd a lot of memory without requiring

			additional memory to do so.

			allocate its internal metadata (struct pages,

			those vmemmap pages cannot be optimized even

			if hugetlb_free_vmemmap is enabled) from the

			hotadded memory which will allow to hotadd a

			lot of memory without requiring additional

			memory to do so.

			This feature is disabled by default because it

			has some implication on large (e.g. GB)

			allocations in some configurations (e.g. small
@@ -3081,10 +3085,6 @@ 
			Note that even when enabled, there are a few cases where

			the feature is not effective.



			This is not compatible with hugetlb_free_vmemmap. If

			both parameters are enabled, hugetlb_free_vmemmap takes

			precedence over memory_hotplug.memmap_on_memory.



	memtest=	[KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest

			Format: <integer>

			default : 0 <disable>

Documentation/admin-guide/sysctl/vm.rst

+2 −3
Original line number Diff line number Diff line
@@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst 
hugetlb_optimize_vmemmap

========================



This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)

is configured or the size of 'struct page' (a structure defined in

include/linux/mm_types.h) is not power of two (an unusual system config could

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

include/linux/memory_hotplug.h

+0 −9
Original line number Diff line number Diff line
@@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size); 
extern bool mhp_supports_memmap_on_memory(unsigned long size);

#endif /* CONFIG_MEMORY_HOTPLUG */



#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY

bool mhp_memmap_on_memory(void);

#else

static inline bool mhp_memmap_on_memory(void)

{

	return false;

}

#endif



#endif /* __LINUX_MEMORY_HOTPLUG_H */

include/linux/page-flags.h

+11 −0
Original line number Diff line number Diff line
@@ -193,6 +193,11 @@ enum pageflags { 


	/* Only valid for buddy pages. Used to track pages that are reported */

	PG_reported = PG_uptodate,



#ifdef CONFIG_MEMORY_HOTPLUG

	/* For self-hosted memmap pages */

	PG_vmemmap_self_hosted = PG_owner_priv_1,

#endif

};



#define PAGEFLAGS_MASK		((1UL << NR_PAGEFLAGS) - 1)
@@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison) 
 */

__PAGEFLAG(Reported, reported, PF_NO_COMPOUND)



#ifdef CONFIG_MEMORY_HOTPLUG

PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)

#else

PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)

#endif



/*

 * On an anonymous page mapped into a user virtual memory area,

 * page->mapping points to its anon_vma, not to a struct address_space;

mm/hugetlb_vmemmap.c

+58 −8
Original line number Diff line number Diff line
@@ -10,7 +10,7 @@ 
 */

#define pr_fmt(fmt)	"HugeTLB: " fmt



#include <linux/memory_hotplug.h>

#include <linux/memory.h>

#include "hugetlb_vmemmap.h"



/*
@@ -97,18 +97,68 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head) 
	return ret;

}



static unsigned int vmemmap_optimizable_pages(struct hstate *h,

					      struct page *head)

{

	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)

		return 0;



	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {

		pmd_t *pmdp, pmd;

		struct page *vmemmap_page;

		unsigned long vaddr = (unsigned long)head;



		/*

		 * Only the vmemmap page's vmemmap page can be self-hosted.

		 * Walking the page tables to find the backing page of the

		 * vmemmap page.

		 */

		pmdp = pmd_off_k(vaddr);

		/*

		 * The READ_ONCE() is used to stabilize *pmdp in a register or

		 * on the stack so that it will stop changing under the code.

		 * The only concurrent operation where it can be changed is

		 * split_vmemmap_huge_pmd() (*pmdp will be stable after this

		 * operation).

		 */

		pmd = READ_ONCE(*pmdp);

		if (pmd_leaf(pmd))

			vmemmap_page = pmd_page(pmd) + pte_index(vaddr);

		else

			vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));

		/*

		 * Due to HugeTLB alignment requirements and the vmemmap pages

		 * being at the start of the hotplugged memory region in

		 * memory_hotplug.memmap_on_memory case. Checking any vmemmap

		 * page's vmemmap page if it is marked as VmemmapSelfHosted is

		 * sufficient.

		 *

		 * [                  hotplugged memory                  ]

		 * [        section        ][...][        section        ]

		 * [ vmemmap ][              usable memory               ]

		 *   ^   |     |                                        |

		 *   +---+     |                                        |

		 *     ^       |                                        |

		 *     +-------+                                        |

		 *          ^                                           |

		 *          +-------------------------------------------+

		 */

		if (PageVmemmapSelfHosted(vmemmap_page))

			return 0;

	}



	return hugetlb_optimize_vmemmap_pages(h);

}



void hugetlb_vmemmap_free(struct hstate *h, struct page *head)

{

	unsigned long vmemmap_addr = (unsigned long)head;

	unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;



	vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);

	vmemmap_pages = vmemmap_optimizable_pages(h, head);

	if (!vmemmap_pages)

		return;



	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)

		return;



	static_branch_inc(&hugetlb_optimize_vmemmap_key);



	vmemmap_addr	+= RESERVE_VMEMMAP_SIZE;
@@ -199,10 +249,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = { 
static __init int hugetlb_vmemmap_sysctls_init(void)

{

	/*

	 * If "memory_hotplug.memmap_on_memory" is enabled or "struct page"

	 * crosses page boundaries, the vmemmap pages cannot be optimized.

	 * If "struct page" crosses page boundaries, the vmemmap pages cannot

	 * be optimized.

	 */

	if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))

	if (is_power_of_2(sizeof(struct page)))

		register_sysctl_init("vm", hugetlb_vmemmap_sysctls);



	return 0;