ksm.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2#ifndef __LINUX_KSM_H
  3#define __LINUX_KSM_H
  4/*
  5 * Memory merging support.
  6 *
  7 * This code enables dynamic sharing of identical pages found in different
  8 * memory areas, even if they are not shared by fork().
  9 */
 10
 11#include <linux/bitops.h>
 12#include <linux/mm.h>
 13#include <linux/pagemap.h>
 14#include <linux/rmap.h>
 15#include <linux/sched.h>
 16
 17#ifdef CONFIG_KSM
 18int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 19		unsigned long end, int advice, vm_flags_t *vm_flags);
 20vm_flags_t ksm_vma_flags(struct mm_struct *mm, const struct file *file,
 21			 vm_flags_t vm_flags);
 22int ksm_enable_merge_any(struct mm_struct *mm);
 23int ksm_disable_merge_any(struct mm_struct *mm);
 24int ksm_disable(struct mm_struct *mm);
 25
 26int __ksm_enter(struct mm_struct *mm);
 27void __ksm_exit(struct mm_struct *mm);
 28/*
 29 * To identify zeropages that were mapped by KSM, we reuse the dirty bit
 30 * in the PTE. If the PTE is dirty, the zeropage was mapped by KSM when
 31 * deduplicating memory.
 32 */
 33#define is_ksm_zero_pte(pte)	(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte))
 34
 35extern atomic_long_t ksm_zero_pages;
 36
 37static inline void ksm_map_zero_page(struct mm_struct *mm)
 38{
 39	atomic_long_inc(&ksm_zero_pages);
 40	atomic_long_inc(&mm->ksm_zero_pages);
 41}
 42
 43static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte)
 44{
 45	if (is_ksm_zero_pte(pte)) {
 46		atomic_long_dec(&ksm_zero_pages);
 47		atomic_long_dec(&mm->ksm_zero_pages);
 48	}
 49}
 50
 51static inline long mm_ksm_zero_pages(struct mm_struct *mm)
 52{
 53	return atomic_long_read(&mm->ksm_zero_pages);
 54}
 55
 56static inline void ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 57{
 58	/* Adding mm to ksm is best effort on fork. */
 59	if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) {
 60		long nr_ksm_zero_pages = atomic_long_read(&mm->ksm_zero_pages);
 61
 62		mm->ksm_merging_pages = 0;
 63		mm->ksm_rmap_items = 0;
 64		atomic_long_add(nr_ksm_zero_pages, &ksm_zero_pages);
 65		__ksm_enter(mm);
 66	}
 67}
 68
 69static inline int ksm_execve(struct mm_struct *mm)
 70{
 71	if (mm_flags_test(MMF_VM_MERGE_ANY, mm))
 72		return __ksm_enter(mm);
 73
 74	return 0;
 75}
 76
 77static inline void ksm_exit(struct mm_struct *mm)
 78{
 79	if (mm_flags_test(MMF_VM_MERGEABLE, mm))
 80		__ksm_exit(mm);
 81}
 82
 83/*
 84 * When do_swap_page() first faults in from swap what used to be a KSM page,
 85 * no problem, it will be assigned to this vma's anon_vma; but thereafter,
 86 * it might be faulted into a different anon_vma (or perhaps to a different
 87 * offset in the same anon_vma).  do_swap_page() cannot do all the locking
 88 * needed to reconstitute a cross-anon_vma KSM page: for now it has to make
 89 * a copy, and leave remerging the pages to a later pass of ksmd.
 90 *
 91 * We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE,
 92 * but what if the vma was unmerged while the page was swapped out?
 93 */
 94struct folio *ksm_might_need_to_copy(struct folio *folio,
 95			struct vm_area_struct *vma, unsigned long addr);
 96
 97void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc);
 98void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
 99void collect_procs_ksm(const struct folio *folio, const struct page *page,
100		struct list_head *to_kill, int force_early);
101long ksm_process_profit(struct mm_struct *);
102bool ksm_process_mergeable(struct mm_struct *mm);
103
104#else  /* !CONFIG_KSM */
105
106static inline vm_flags_t ksm_vma_flags(struct mm_struct *mm,
107		const struct file *file, vm_flags_t vm_flags)
108{
109	return vm_flags;
110}
111
112static inline int ksm_disable(struct mm_struct *mm)
113{
114	return 0;
115}
116
117static inline void ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
118{
119}
120
121static inline int ksm_execve(struct mm_struct *mm)
122{
123	return 0;
124}
125
126static inline void ksm_exit(struct mm_struct *mm)
127{
128}
129
130static inline void ksm_might_unmap_zero_page(struct mm_struct *mm, pte_t pte)
131{
132}
133
134static inline void collect_procs_ksm(const struct folio *folio,
135		const struct page *page, struct list_head *to_kill,
136		int force_early)
137{
138}
139
140#ifdef CONFIG_MMU
141static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
142		unsigned long end, int advice, vm_flags_t *vm_flags)
143{
144	return 0;
145}
146
147static inline struct folio *ksm_might_need_to_copy(struct folio *folio,
148			struct vm_area_struct *vma, unsigned long addr)
149{
150	return folio;
151}
152
153static inline void rmap_walk_ksm(struct folio *folio,
154			struct rmap_walk_control *rwc)
155{
156}
157
158static inline void folio_migrate_ksm(struct folio *newfolio, struct folio *old)
159{
160}
161#endif /* CONFIG_MMU */
162#endif /* !CONFIG_KSM */
163
164#endif /* __LINUX_KSM_H */