xref: /linux/mm/swap_table.h (revision 8804d970fab45726b3c7cd7f240b31122aa94219)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _MM_SWAP_TABLE_H
3 #define _MM_SWAP_TABLE_H
4 
5 #include <linux/rcupdate.h>
6 #include <linux/atomic.h>
7 #include "swap.h"
8 
9 /* A typical flat array in each cluster as swap table */
10 struct swap_table {
11 	atomic_long_t entries[SWAPFILE_CLUSTER];
12 };
13 
14 #define SWP_TABLE_USE_PAGE (sizeof(struct swap_table) == PAGE_SIZE)
15 
16 /*
17  * A swap table entry represents the status of a swap slot on a swap
18  * (physical or virtual) device. The swap table in each cluster is a
19  * 1:1 map of the swap slots in this cluster.
20  *
21  * Each swap table entry could be a pointer (folio), a XA_VALUE
22  * (shadow), or NULL.
23  */
24 
25 /*
26  * Helpers for casting one type of info into a swap table entry.
27  */
null_to_swp_tb(void)28 static inline unsigned long null_to_swp_tb(void)
29 {
30 	BUILD_BUG_ON(sizeof(unsigned long) != sizeof(atomic_long_t));
31 	return 0;
32 }
33 
folio_to_swp_tb(struct folio * folio)34 static inline unsigned long folio_to_swp_tb(struct folio *folio)
35 {
36 	BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void *));
37 	return (unsigned long)folio;
38 }
39 
shadow_swp_to_tb(void * shadow)40 static inline unsigned long shadow_swp_to_tb(void *shadow)
41 {
42 	BUILD_BUG_ON((BITS_PER_XA_VALUE + 1) !=
43 		     BITS_PER_BYTE * sizeof(unsigned long));
44 	VM_WARN_ON_ONCE(shadow && !xa_is_value(shadow));
45 	return (unsigned long)shadow;
46 }
47 
48 /*
49  * Helpers for swap table entry type checking.
50  */
swp_tb_is_null(unsigned long swp_tb)51 static inline bool swp_tb_is_null(unsigned long swp_tb)
52 {
53 	return !swp_tb;
54 }
55 
swp_tb_is_folio(unsigned long swp_tb)56 static inline bool swp_tb_is_folio(unsigned long swp_tb)
57 {
58 	return !xa_is_value((void *)swp_tb) && !swp_tb_is_null(swp_tb);
59 }
60 
swp_tb_is_shadow(unsigned long swp_tb)61 static inline bool swp_tb_is_shadow(unsigned long swp_tb)
62 {
63 	return xa_is_value((void *)swp_tb);
64 }
65 
66 /*
67  * Helpers for retrieving info from swap table.
68  */
swp_tb_to_folio(unsigned long swp_tb)69 static inline struct folio *swp_tb_to_folio(unsigned long swp_tb)
70 {
71 	VM_WARN_ON(!swp_tb_is_folio(swp_tb));
72 	return (void *)swp_tb;
73 }
74 
swp_tb_to_shadow(unsigned long swp_tb)75 static inline void *swp_tb_to_shadow(unsigned long swp_tb)
76 {
77 	VM_WARN_ON(!swp_tb_is_shadow(swp_tb));
78 	return (void *)swp_tb;
79 }
80 
81 /*
82  * Helpers for accessing or modifying the swap table of a cluster,
83  * the swap cluster must be locked.
84  */
__swap_table_set(struct swap_cluster_info * ci,unsigned int off,unsigned long swp_tb)85 static inline void __swap_table_set(struct swap_cluster_info *ci,
86 				    unsigned int off, unsigned long swp_tb)
87 {
88 	atomic_long_t *table = rcu_dereference_protected(ci->table, true);
89 
90 	lockdep_assert_held(&ci->lock);
91 	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
92 	atomic_long_set(&table[off], swp_tb);
93 }
94 
__swap_table_xchg(struct swap_cluster_info * ci,unsigned int off,unsigned long swp_tb)95 static inline unsigned long __swap_table_xchg(struct swap_cluster_info *ci,
96 					      unsigned int off, unsigned long swp_tb)
97 {
98 	atomic_long_t *table = rcu_dereference_protected(ci->table, true);
99 
100 	lockdep_assert_held(&ci->lock);
101 	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
102 	/* Ordering is guaranteed by cluster lock, relax */
103 	return atomic_long_xchg_relaxed(&table[off], swp_tb);
104 }
105 
__swap_table_get(struct swap_cluster_info * ci,unsigned int off)106 static inline unsigned long __swap_table_get(struct swap_cluster_info *ci,
107 					     unsigned int off)
108 {
109 	atomic_long_t *table;
110 
111 	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
112 	table = rcu_dereference_check(ci->table, lockdep_is_held(&ci->lock));
113 
114 	return atomic_long_read(&table[off]);
115 }
116 
swap_table_get(struct swap_cluster_info * ci,unsigned int off)117 static inline unsigned long swap_table_get(struct swap_cluster_info *ci,
118 					unsigned int off)
119 {
120 	atomic_long_t *table;
121 	unsigned long swp_tb;
122 
123 	rcu_read_lock();
124 	table = rcu_dereference(ci->table);
125 	swp_tb = table ? atomic_long_read(&table[off]) : null_to_swp_tb();
126 	rcu_read_unlock();
127 
128 	return swp_tb;
129 }
130 #endif
131