2 * Compressed RAM block device
4 * Copyright (C) 2008, 2009, 2010 Nitin Gupta
5 * 2012, 2013 Minchan Kim
7 * This code is released using a dual license strategy: BSD/GPL
8 * You can choose the licence that better fits your requirements.
10 * Released under the terms of 3-clause BSD License
11 * Released under the terms of GNU General Public License Version 2.0
18 #include <linux/spinlock.h>
19 #include <linux/zsmalloc.h>
24 * Some arbitrary value. This is just to catch
25 * invalid value for num_devices module parameter.
27 static const unsigned max_num_devices = 32;
29 /*-- Configurable parameters */
32 * Pages that compress to size greater than this are stored
33 * uncompressed in memory.
35 static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
38 * NOTE: max_zpage_size must be less than or equal to:
39 * ZS_MAX_ALLOC_SIZE. Otherwise, zs_malloc() would
40 * always return failure.
43 /*-- End of configurable params */
45 #define SECTOR_SHIFT 9
46 #define SECTORS_PER_PAGE_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
47 #define SECTORS_PER_PAGE (1 << SECTORS_PER_PAGE_SHIFT)
48 #define ZRAM_LOGICAL_BLOCK_SHIFT 12
49 #define ZRAM_LOGICAL_BLOCK_SIZE (1 << ZRAM_LOGICAL_BLOCK_SHIFT)
50 #define ZRAM_SECTOR_PER_LOGICAL_BLOCK \
51 (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
55 * The lower ZRAM_FLAG_SHIFT bits of table.value is for
56 * object size (excluding header), the higher bits is for
59 * zram is mainly used for memory efficiency so we want to keep memory
60 * footprint small so we can squeeze size and flags into a field.
61 * The lower ZRAM_FLAG_SHIFT bits is for object size (excluding header),
62 * the higher bits is for zram_pageflags.
64 #define ZRAM_FLAG_SHIFT 24
66 /* Flags for zram pages (table[page_no].value) */
68 /* Page consists entirely of zeros */
69 ZRAM_ZERO = ZRAM_FLAG_SHIFT,
70 ZRAM_ACCESS, /* page is now accessed */
75 /*-- Data structures */
77 /* Allocated for each disk page */
78 struct zram_table_entry {
84 atomic64_t compr_data_size; /* compressed size of pages stored */
85 atomic64_t num_reads; /* failed + successful */
86 atomic64_t num_writes; /* --do-- */
87 atomic64_t num_migrated; /* no. of migrated object */
88 atomic64_t failed_reads; /* can happen when memory is too low */
89 atomic64_t failed_writes; /* can happen when memory is too low */
90 atomic64_t invalid_io; /* non-page-aligned I/O requests */
91 atomic64_t notify_free; /* no. of swap slot free notifications */
92 atomic64_t zero_pages; /* no. of zero filled pages */
93 atomic64_t pages_stored; /* no. of pages currently stored */
94 atomic_long_t max_used_pages; /* no. of maximum pages stored */
98 struct zram_table_entry *table;
99 struct zs_pool *mem_pool;
103 struct zram_meta *meta;
105 struct gendisk *disk;
106 /* Prevent concurrent execution of device init */
107 struct rw_semaphore init_lock;
109 * the number of pages zram can consume for storing compressed data
111 unsigned long limit_pages;
112 int max_comp_streams;
114 struct zram_stats stats;
115 atomic_t refcount; /* refcount for zram_meta */
116 /* wait all IO under all of cpu are done */
117 wait_queue_head_t io_done;
119 * This is the limit on amount of *uncompressed* worth of data
120 * we can store in a disk.
122 u64 disksize; /* bytes */