xref: /linux/drivers/block/zram/zram_drv.h (revision 507e190946297c34a27d9366b0661d5e506fdd03)
1 /*
2  * Compressed RAM block device
3  *
4  * Copyright (C) 2008, 2009, 2010  Nitin Gupta
5  *               2012, 2013 Minchan Kim
6  *
7  * This code is released using a dual license strategy: BSD/GPL
8  * You can choose the licence that better fits your requirements.
9  *
10  * Released under the terms of 3-clause BSD License
11  * Released under the terms of GNU General Public License Version 2.0
12  *
13  */
14 
15 #ifndef _ZRAM_DRV_H_
16 #define _ZRAM_DRV_H_
17 
18 #include <linux/rwsem.h>
19 #include <linux/zsmalloc.h>
20 #include <linux/crypto.h>
21 
22 #include "zcomp.h"
23 
24 /*-- Configurable parameters */
25 
26 /*
27  * Pages that compress to size greater than this are stored
28  * uncompressed in memory.
29  */
30 static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
31 
32 /*
33  * NOTE: max_zpage_size must be less than or equal to:
34  *   ZS_MAX_ALLOC_SIZE. Otherwise, zs_malloc() would
35  * always return failure.
36  */
37 
38 /*-- End of configurable params */
39 
40 #define SECTOR_SHIFT		9
41 #define SECTORS_PER_PAGE_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
42 #define SECTORS_PER_PAGE	(1 << SECTORS_PER_PAGE_SHIFT)
43 #define ZRAM_LOGICAL_BLOCK_SHIFT 12
44 #define ZRAM_LOGICAL_BLOCK_SIZE	(1 << ZRAM_LOGICAL_BLOCK_SHIFT)
45 #define ZRAM_SECTOR_PER_LOGICAL_BLOCK	\
46 	(1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
47 
48 
49 /*
50  * The lower ZRAM_FLAG_SHIFT bits of table.value is for
51  * object size (excluding header), the higher bits is for
52  * zram_pageflags.
53  *
54  * zram is mainly used for memory efficiency so we want to keep memory
55  * footprint small so we can squeeze size and flags into a field.
56  * The lower ZRAM_FLAG_SHIFT bits is for object size (excluding header),
57  * the higher bits is for zram_pageflags.
58  */
59 #define ZRAM_FLAG_SHIFT 24
60 
61 /* Flags for zram pages (table[page_no].value) */
62 enum zram_pageflags {
63 	/* Page consists entirely of zeros */
64 	ZRAM_SAME = ZRAM_FLAG_SHIFT,
65 	ZRAM_ACCESS,	/* page is now accessed */
66 
67 	__NR_ZRAM_PAGEFLAGS,
68 };
69 
70 /*-- Data structures */
71 
72 /* Allocated for each disk page */
73 struct zram_table_entry {
74 	union {
75 		unsigned long handle;
76 		unsigned long element;
77 	};
78 	unsigned long value;
79 };
80 
81 struct zram_stats {
82 	atomic64_t compr_data_size;	/* compressed size of pages stored */
83 	atomic64_t num_reads;	/* failed + successful */
84 	atomic64_t num_writes;	/* --do-- */
85 	atomic64_t failed_reads;	/* can happen when memory is too low */
86 	atomic64_t failed_writes;	/* can happen when memory is too low */
87 	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
88 	atomic64_t notify_free;	/* no. of swap slot free notifications */
89 	atomic64_t same_pages;		/* no. of same element filled pages */
90 	atomic64_t pages_stored;	/* no. of pages currently stored */
91 	atomic_long_t max_used_pages;	/* no. of maximum pages stored */
92 	atomic64_t writestall;		/* no. of write slow paths */
93 };
94 
95 struct zram {
96 	struct zram_table_entry *table;
97 	struct zs_pool *mem_pool;
98 	struct zcomp *comp;
99 	struct gendisk *disk;
100 	/* Prevent concurrent execution of device init */
101 	struct rw_semaphore init_lock;
102 	/*
103 	 * the number of pages zram can consume for storing compressed data
104 	 */
105 	unsigned long limit_pages;
106 
107 	struct zram_stats stats;
108 	/*
109 	 * This is the limit on amount of *uncompressed* worth of data
110 	 * we can store in a disk.
111 	 */
112 	u64 disksize;	/* bytes */
113 	char compressor[CRYPTO_MAX_ALG_NAME];
114 	/*
115 	 * zram is claimed so open request will be failed
116 	 */
117 	bool claim; /* Protected by bdev->bd_mutex */
118 };
119 #endif
120