mm/zpdesc.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /* zpdesc.h: zswap.zpool 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 /*
  11  * struct zpdesc -      Memory descriptor for zpool memory.
  12  * @flags:              Page flags, mostly unused by zsmalloc.
  13  * @lru:                Indirectly used by page migration.
  14  * @movable_ops:        Used by page migration.
  15  * @next:               Next zpdesc in a zspage in zsmalloc zpool.
  16  * @handle:             For huge zspage in zsmalloc zpool.
  17  * @zspage:             Points to the zspage this zpdesc is a part of.
  18  * @first_obj_offset:   First object offset in zsmalloc zpool.
  19  * @_refcount:          The number of references to this zpdesc.
  20  *
  21  * This struct overlays struct page for now. Do not modify without a good
  22  * understanding of the issues. In particular, do not expand into the overlap
  23  * with memcg_data.
  24  *
  25  * Page flags used:
  26  * * PG_private identifies the first component page.
  27  * * PG_locked is used by page migration code.
  28  */
  29 struct zpdesc {
  30         unsigned long flags;
  31         struct list_head lru;
  32         unsigned long movable_ops;
  33         union {
  34                 struct zpdesc *next;
  35                 unsigned long handle;
  36         };
  37         struct zspage *zspage;
  38         /*
  39          * Only the lower 24 bits are available for offset, limiting a page
  40          * to 16 MiB. The upper 8 bits are reserved for PGTY_zsmalloc.
  41          *
  42          * Do not access this field directly.
  43          * Instead, use {get,set}_first_obj_offset() helpers.
  44          */
  45         unsigned int first_obj_offset;
  46         atomic_t _refcount;
  47 };
  48 #define ZPDESC_MATCH(pg, zp) \
  49         static_assert(offsetof(struct page, pg) == offsetof(struct zpdesc, zp))
  50
  51 ZPDESC_MATCH(flags, flags);
  52 ZPDESC_MATCH(lru, lru);
  53 ZPDESC_MATCH(mapping, movable_ops);
  54 ZPDESC_MATCH(index, next);
  55 ZPDESC_MATCH(index, handle);
  56 ZPDESC_MATCH(private, zspage);
  57 ZPDESC_MATCH(page_type, first_obj_offset);
  58 ZPDESC_MATCH(_refcount, _refcount);
  59 #undef ZPDESC_MATCH
  60 static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
  61
  62 /*
  63  * zpdesc_page - The first struct page allocated for a zpdesc
  64  * @zp: The zpdesc.
  65  *
  66  * A convenience wrapper for converting zpdesc to the first struct page of the
  67  * underlying folio, to communicate with code not yet converted to folio or
  68  * struct zpdesc.
  69  *
  70  */
  71 #define zpdesc_page(zp)                 (_Generic((zp),                 \
  72         const struct zpdesc *:          (const struct page *)(zp),      \
  73         struct zpdesc *:                (struct page *)(zp)))
  74
  75 /**
  76  * zpdesc_folio - The folio allocated for a zpdesc
  77  * @zp: The zpdesc.
  78  *
  79  * Zpdescs are descriptors for zpool memory. The zpool memory itself is
  80  * allocated as folios that contain the zpool objects, and zpdesc uses specific
  81  * fields in the first struct page of the folio - those fields are now accessed
  82  * by struct zpdesc.
  83  *
  84  * It is occasionally necessary convert to back to a folio in order to
  85  * communicate with the rest of the mm. Please use this helper function
  86  * instead of casting yourself, as the implementation may change in the future.
  87  */
  88 #define zpdesc_folio(zp)                (_Generic((zp),                 \
  89         const struct zpdesc *:          (const struct folio *)(zp),     \
  90         struct zpdesc *:                (struct folio *)(zp)))
  91 /**
  92  * page_zpdesc - Converts from first struct page to zpdesc.
  93  * @p: The first (either head of compound or single) page of zpdesc.
  94  *
  95  * A temporary wrapper to convert struct page to struct zpdesc in situations
  96  * where we know the page is the compound head, or single order-0 page.
  97  *
  98  * Long-term ideally everything would work with struct zpdesc directly or go
  99  * through folio to struct zpdesc.
 100  *
 101  * Return: The zpdesc which contains this page
 102  */
 103 #define page_zpdesc(p)                  (_Generic((p),                  \
 104         const struct page *:            (const struct zpdesc *)(p),     \
 105         struct page *:                  (struct zpdesc *)(p)))
 106
 107 static inline void zpdesc_lock(struct zpdesc *zpdesc)
 108 {
 109         folio_lock(zpdesc_folio(zpdesc));
 110 }
 111
 112 static inline bool zpdesc_trylock(struct zpdesc *zpdesc)
 113 {
 114         return folio_trylock(zpdesc_folio(zpdesc));
 115 }
 116
 117 static inline void zpdesc_unlock(struct zpdesc *zpdesc)
 118 {
 119         folio_unlock(zpdesc_folio(zpdesc));
 120 }
 121
 122 static inline void zpdesc_wait_locked(struct zpdesc *zpdesc)
 123 {
 124         folio_wait_locked(zpdesc_folio(zpdesc));
 125 }
 126
 127 static inline void zpdesc_get(struct zpdesc *zpdesc)
 128 {
 129         folio_get(zpdesc_folio(zpdesc));
 130 }
 131
 132 static inline void zpdesc_put(struct zpdesc *zpdesc)
 133 {
 134         folio_put(zpdesc_folio(zpdesc));
 135 }
 136
 137 static inline void *kmap_local_zpdesc(struct zpdesc *zpdesc)
 138 {
 139         return kmap_local_page(zpdesc_page(zpdesc));
 140 }
 141
 142 static inline unsigned long zpdesc_pfn(struct zpdesc *zpdesc)
 143 {
 144         return page_to_pfn(zpdesc_page(zpdesc));
 145 }
 146
 147 static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
 148 {
 149         return page_zpdesc(pfn_to_page(pfn));
 150 }
 151
 152 static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
 153                                         const struct movable_operations *mops)
 154 {
 155         __SetPageMovable(zpdesc_page(zpdesc), mops);
 156 }
 157
 158 static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
 159 {
 160         __SetPageZsmalloc(zpdesc_page(zpdesc));
 161 }
 162
 163 static inline void __zpdesc_clear_zsmalloc(struct zpdesc *zpdesc)
 164 {
 165         __ClearPageZsmalloc(zpdesc_page(zpdesc));
 166 }
 167
 168 static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
 169 {
 170         return PageIsolated(zpdesc_page(zpdesc));
 171 }
 172
 173 static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
 174 {
 175         return page_zone(zpdesc_page(zpdesc));
 176 }
 177
 178 static inline bool zpdesc_is_locked(struct zpdesc *zpdesc)
 179 {
 180         return folio_test_locked(zpdesc_folio(zpdesc));
 181 }
 182 #endif