diff options
Diffstat (limited to 'mm/swap_table.h')
| -rw-r--r-- | mm/swap_table.h | 138 |
1 files changed, 129 insertions, 9 deletions
diff --git a/mm/swap_table.h b/mm/swap_table.h index ea244a57a5b7..8415ffbe2b9c 100644 --- a/mm/swap_table.h +++ b/mm/swap_table.h @@ -18,10 +18,69 @@ struct swap_table { * (physical or virtual) device. The swap table in each cluster is a * 1:1 map of the swap slots in this cluster. * - * Each swap table entry could be a pointer (folio), a XA_VALUE - * (shadow), or NULL. + * Swap table entry type and bits layouts: + * + * NULL: |---------------- 0 ---------------| - Free slot + * Shadow: | SWAP_COUNT |---- SHADOW_VAL ---|1| - Swapped out slot + * PFN: | SWAP_COUNT |------ PFN -------|10| - Cached slot + * Pointer: |----------- Pointer ----------|100| - (Unused) + * Bad: |------------- 1 -------------|1000| - Bad slot + * + * SWAP_COUNT is `SWP_TB_COUNT_BITS` long, each entry is an atomic long. + * + * Usages: + * + * - NULL: Swap slot is unused, could be allocated. + * + * - Shadow: Swap slot is used and not cached (usually swapped out). It reuses + * the XA_VALUE format to be compatible with working set shadows. SHADOW_VAL + * part might be all 0 if the working shadow info is absent. In such a case, + * we still want to keep the shadow format as a placeholder. + * + * Memcg ID is embedded in SHADOW_VAL. + * + * - PFN: Swap slot is in use, and cached. Memcg info is recorded on the page + * struct. + * + * - Pointer: Unused yet. `0b100` is reserved for potential pointer usage + * because only the lower three bits can be used as a marker for 8 bytes + * aligned pointers. + * + * - Bad: Swap slot is reserved, protects swap header or holes on swap devices. */ +#if defined(MAX_POSSIBLE_PHYSMEM_BITS) +#define SWAP_CACHE_PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT) +#elif defined(MAX_PHYSMEM_BITS) +#define SWAP_CACHE_PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT) +#else +#define SWAP_CACHE_PFN_BITS (BITS_PER_LONG - PAGE_SHIFT) +#endif + +/* NULL Entry, all 0 */ +#define SWP_TB_NULL 0UL + +/* Swapped out: shadow */ +#define SWP_TB_SHADOW_MARK 0b1UL + +/* Cached: PFN */ +#define SWP_TB_PFN_BITS (SWAP_CACHE_PFN_BITS + SWP_TB_PFN_MARK_BITS) +#define SWP_TB_PFN_MARK 0b10UL +#define SWP_TB_PFN_MARK_BITS 2 +#define SWP_TB_PFN_MARK_MASK (BIT(SWP_TB_PFN_MARK_BITS) - 1) + +/* SWAP_COUNT part for PFN or shadow, the width can be shrunk or extended */ +#define SWP_TB_COUNT_BITS min(4, BITS_PER_LONG - SWP_TB_PFN_BITS) +#define SWP_TB_COUNT_MASK (~((~0UL) >> SWP_TB_COUNT_BITS)) +#define SWP_TB_COUNT_SHIFT (BITS_PER_LONG - SWP_TB_COUNT_BITS) +#define SWP_TB_COUNT_MAX ((1 << SWP_TB_COUNT_BITS) - 1) + +/* Bad slot: ends with 0b1000 and rests of bits are all 1 */ +#define SWP_TB_BAD ((~0UL) << 3) + +/* Macro for shadow offset calculation */ +#define SWAP_COUNT_SHIFT SWP_TB_COUNT_BITS + /* * Helpers for casting one type of info into a swap table entry. */ @@ -31,18 +90,47 @@ static inline unsigned long null_to_swp_tb(void) return 0; } -static inline unsigned long folio_to_swp_tb(struct folio *folio) +static inline unsigned long __count_to_swp_tb(unsigned char count) { + /* + * At least three values are needed to distinguish free (0), + * used (count > 0 && count < SWP_TB_COUNT_MAX), and + * overflow (count == SWP_TB_COUNT_MAX). + */ + BUILD_BUG_ON(SWP_TB_COUNT_MAX < 2 || SWP_TB_COUNT_BITS < 2); + VM_WARN_ON(count > SWP_TB_COUNT_MAX); + return ((unsigned long)count) << SWP_TB_COUNT_SHIFT; +} + +static inline unsigned long pfn_to_swp_tb(unsigned long pfn, unsigned int count) +{ + unsigned long swp_tb; + BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void *)); - return (unsigned long)folio; + BUILD_BUG_ON(SWAP_CACHE_PFN_BITS > + (BITS_PER_LONG - SWP_TB_PFN_MARK_BITS - SWP_TB_COUNT_BITS)); + + swp_tb = (pfn << SWP_TB_PFN_MARK_BITS) | SWP_TB_PFN_MARK; + VM_WARN_ON_ONCE(swp_tb & SWP_TB_COUNT_MASK); + + return swp_tb | __count_to_swp_tb(count); +} + +static inline unsigned long folio_to_swp_tb(struct folio *folio, unsigned int count) +{ + return pfn_to_swp_tb(folio_pfn(folio), count); } -static inline unsigned long shadow_swp_to_tb(void *shadow) +static inline unsigned long shadow_to_swp_tb(void *shadow, unsigned int count) { BUILD_BUG_ON((BITS_PER_XA_VALUE + 1) != BITS_PER_BYTE * sizeof(unsigned long)); + BUILD_BUG_ON((unsigned long)xa_mk_value(0) != SWP_TB_SHADOW_MARK); + VM_WARN_ON_ONCE(shadow && !xa_is_value(shadow)); - return (unsigned long)shadow; + VM_WARN_ON_ONCE(shadow && ((unsigned long)shadow & SWP_TB_COUNT_MASK)); + + return (unsigned long)shadow | __count_to_swp_tb(count) | SWP_TB_SHADOW_MARK; } /* @@ -55,7 +143,7 @@ static inline bool swp_tb_is_null(unsigned long swp_tb) static inline bool swp_tb_is_folio(unsigned long swp_tb) { - return !xa_is_value((void *)swp_tb) && !swp_tb_is_null(swp_tb); + return ((swp_tb & SWP_TB_PFN_MARK_MASK) == SWP_TB_PFN_MARK); } static inline bool swp_tb_is_shadow(unsigned long swp_tb) @@ -63,19 +151,49 @@ static inline bool swp_tb_is_shadow(unsigned long swp_tb) return xa_is_value((void *)swp_tb); } +static inline bool swp_tb_is_bad(unsigned long swp_tb) +{ + return swp_tb == SWP_TB_BAD; +} + +static inline bool swp_tb_is_countable(unsigned long swp_tb) +{ + return (swp_tb_is_shadow(swp_tb) || swp_tb_is_folio(swp_tb) || + swp_tb_is_null(swp_tb)); +} + /* * Helpers for retrieving info from swap table. */ static inline struct folio *swp_tb_to_folio(unsigned long swp_tb) { VM_WARN_ON(!swp_tb_is_folio(swp_tb)); - return (void *)swp_tb; + return pfn_folio((swp_tb & ~SWP_TB_COUNT_MASK) >> SWP_TB_PFN_MARK_BITS); } static inline void *swp_tb_to_shadow(unsigned long swp_tb) { VM_WARN_ON(!swp_tb_is_shadow(swp_tb)); - return (void *)swp_tb; + /* No shift needed, xa_value is stored as it is in the lower bits. */ + return (void *)(swp_tb & ~SWP_TB_COUNT_MASK); +} + +static inline unsigned char __swp_tb_get_count(unsigned long swp_tb) +{ + VM_WARN_ON(!swp_tb_is_countable(swp_tb)); + return ((swp_tb & SWP_TB_COUNT_MASK) >> SWP_TB_COUNT_SHIFT); +} + +static inline int swp_tb_get_count(unsigned long swp_tb) +{ + if (swp_tb_is_countable(swp_tb)) + return __swp_tb_get_count(swp_tb); + return -EINVAL; +} + +static inline unsigned long __swp_tb_mk_count(unsigned long swp_tb, int count) +{ + return ((swp_tb & ~SWP_TB_COUNT_MASK) | __count_to_swp_tb(count)); } /* @@ -120,6 +238,8 @@ static inline unsigned long swap_table_get(struct swap_cluster_info *ci, atomic_long_t *table; unsigned long swp_tb; + VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER); + rcu_read_lock(); table = rcu_dereference(ci->table); swp_tb = table ? atomic_long_read(&table[off]) : null_to_swp_tb(); |