1/* SPDX-License-Identifier: GPL-2.0 */
2/* zpdesc.h: zsmalloc pool memory descriptor
3 *
4 * Written by Alex Shi <alexs@kernel.org>
5 * Hyeonggon Yoo <42.hyeyoo@gmail.com>
6 */
7#ifndef __MM_ZPDESC_H__
8#define __MM_ZPDESC_H__
9
10#include <linux/migrate.h>
11#include <linux/pagemap.h>
12
13/*
14 * struct zpdesc - Memory descriptor for zsmalloc pool memory.
15 * @flags: Page flags, mostly unused by zsmalloc.
16 * @lru: Indirectly used by page migration.
17 * @movable_ops: Used by page migration.
18 * @next: Next zpdesc in a zspage in zsmalloc pool.
19 * @handle: For huge zspage in zsmalloc pool.
20 * @zspage: Points to the zspage this zpdesc is a part of.
21 * @first_obj_offset: First object offset in zsmalloc pool.
22 * @_refcount: The number of references to this zpdesc.
23 *
24 * This struct overlays struct page for now. Do not modify without a good
25 * understanding of the issues. In particular, do not expand into the overlap
26 * with memcg_data.
27 *
28 * Page flags used:
29 * * PG_private identifies the first component page.
30 * * PG_locked is used by page migration code.
31 */
32struct zpdesc {
33 unsigned long flags;
34 struct list_head lru;
35 unsigned long movable_ops;
36 union {
37 struct zpdesc *next;
38 unsigned long handle;
39 };
40 struct zspage *zspage;
41 /*
42 * Only the lower 24 bits are available for offset, limiting a page
43 * to 16 MiB. The upper 8 bits are reserved for PGTY_zsmalloc.
44 *
45 * Do not access this field directly.
46 * Instead, use {get,set}_first_obj_offset() helpers.
47 */
48 unsigned int first_obj_offset;
49 atomic_t _refcount;
50};
51#define ZPDESC_MATCH(pg, zp) \
52 static_assert(offsetof(struct page, pg) == offsetof(struct zpdesc, zp))
53
54ZPDESC_MATCH(flags, flags);
55ZPDESC_MATCH(lru, lru);
56ZPDESC_MATCH(mapping, movable_ops);
57ZPDESC_MATCH(__folio_index, next);
58ZPDESC_MATCH(__folio_index, handle);
59ZPDESC_MATCH(private, zspage);
60ZPDESC_MATCH(page_type, first_obj_offset);
61ZPDESC_MATCH(_refcount, _refcount);
62#undef ZPDESC_MATCH
63static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
64
65/*
66 * zpdesc_page - The first struct page allocated for a zpdesc
67 * @zp: The zpdesc.
68 *
69 * A convenience wrapper for converting zpdesc to the first struct page of the
70 * underlying folio, to communicate with code not yet converted to folio or
71 * struct zpdesc.
72 *
73 */
74#define zpdesc_page(zp) (_Generic((zp), \
75 const struct zpdesc *: (const struct page *)(zp), \
76 struct zpdesc *: (struct page *)(zp)))
77
78/**
79 * zpdesc_folio - The folio allocated for a zpdesc
80 * @zp: The zpdesc.
81 *
82 * Zpdescs are descriptors for zsmalloc memory. The memory itself is allocated
83 * as folios that contain the zsmalloc objects, and zpdesc uses specific
84 * fields in the first struct page of the folio - those fields are now accessed
85 * by struct zpdesc.
86 *
87 * It is occasionally necessary convert to back to a folio in order to
88 * communicate with the rest of the mm. Please use this helper function
89 * instead of casting yourself, as the implementation may change in the future.
90 */
91#define zpdesc_folio(zp) (_Generic((zp), \
92 const struct zpdesc *: (const struct folio *)(zp), \
93 struct zpdesc *: (struct folio *)(zp)))
94/**
95 * page_zpdesc - Converts from first struct page to zpdesc.
96 * @p: The first (either head of compound or single) page of zpdesc.
97 *
98 * A temporary wrapper to convert struct page to struct zpdesc in situations
99 * where we know the page is the compound head, or single order-0 page.
100 *
101 * Long-term ideally everything would work with struct zpdesc directly or go
102 * through folio to struct zpdesc.
103 *
104 * Return: The zpdesc which contains this page
105 */
106#define page_zpdesc(p) (_Generic((p), \
107 const struct page *: (const struct zpdesc *)(p), \
108 struct page *: (struct zpdesc *)(p)))
109
110static inline void zpdesc_lock(struct zpdesc *zpdesc)
111{
112 folio_lock(zpdesc_folio(zpdesc));
113}
114
115static inline bool zpdesc_trylock(struct zpdesc *zpdesc)
116{
117 return folio_trylock(zpdesc_folio(zpdesc));
118}
119
120static inline void zpdesc_unlock(struct zpdesc *zpdesc)
121{
122 folio_unlock(zpdesc_folio(zpdesc));
123}
124
125static inline void zpdesc_wait_locked(struct zpdesc *zpdesc)
126{
127 folio_wait_locked(zpdesc_folio(zpdesc));
128}
129
130static inline void zpdesc_get(struct zpdesc *zpdesc)
131{
132 folio_get(zpdesc_folio(zpdesc));
133}
134
135static inline void zpdesc_put(struct zpdesc *zpdesc)
136{
137 folio_put(zpdesc_folio(zpdesc));
138}
139
140static inline void *kmap_local_zpdesc(struct zpdesc *zpdesc)
141{
142 return kmap_local_page(zpdesc_page(zpdesc));
143}
144
145static inline unsigned long zpdesc_pfn(struct zpdesc *zpdesc)
146{
147 return page_to_pfn(zpdesc_page(zpdesc));
148}
149
150static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
151{
152 return page_zpdesc(pfn_to_page(pfn));
153}
154
155static inline void __zpdesc_set_movable(struct zpdesc *zpdesc)
156{
157 SetPageMovableOps(zpdesc_page(zpdesc));
158}
159
160static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
161{
162 __SetPageZsmalloc(zpdesc_page(zpdesc));
163}
164
165static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
166{
167 return page_zone(zpdesc_page(zpdesc));
168}
169
170static inline bool zpdesc_is_locked(struct zpdesc *zpdesc)
171{
172 return folio_test_locked(zpdesc_folio(zpdesc));
173}
174#endif
175

source code of linux/mm/zpdesc.h