swap_table.h

  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 */
 10struct 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 */
 28static 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
 34static 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
 40static 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 */
 51static inline bool swp_tb_is_null(unsigned long swp_tb)
 52{
 53	return !swp_tb;
 54}
 55
 56static 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
 61static 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 */
 69static 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
 75static 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 */
 85static 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
 95static 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
106static 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
117static 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