drivers/staging/zram/zram_drv.h

   1 /*
   2  * Compressed RAM block device
   3  *
   4  * Copyright (C) 2008, 2009, 2010  Nitin Gupta
   5  *
   6  * This code is released using a dual license strategy: BSD/GPL
   7  * You can choose the licence that better fits your requirements.
   8  *
   9  * Released under the terms of 3-clause BSD License
  10  * Released under the terms of GNU General Public License Version 2.0
  11  *
  12  * Project home: http://compcache.googlecode.com
  13  */
  14
  15 #ifndef _ZRAM_DRV_H_
  16 #define _ZRAM_DRV_H_
  17
  18 #include <linux/spinlock.h>
  19 #include <linux/mutex.h>
  20
  21 #include "xvmalloc.h"
  22
  23 /*
  24  * Some arbitrary value. This is just to catch
  25  * invalid value for num_devices module parameter.
  26  */
  27 static const unsigned max_num_devices = 32;
  28
  29 /*
  30  * Stored at beginning of each compressed object.
  31  *
  32  * It stores back-reference to table entry which points to this
  33  * object. This is required to support memory defragmentation.
  34  */
  35 struct zobj_header {
  36 #if 0
  37         u32 table_idx;
  38 #endif
  39 };
  40
  41 /*-- Configurable parameters */
  42
  43 /* Default zram disk size: 25% of total RAM */
  44 static const unsigned default_disksize_perc_ram = 25;
  45
  46 /*
  47  * Pages that compress to size greater than this are stored
  48  * uncompressed in memory.
  49  */
  50 static const unsigned max_zpage_size = PAGE_SIZE / 4 * 3;
  51
  52 /*
  53  * NOTE: max_zpage_size must be less than or equal to:
  54  *   XV_MAX_ALLOC_SIZE - sizeof(struct zobj_header)
  55  * otherwise, xv_malloc() would always return failure.
  56  */
  57
  58 /*-- End of configurable params */
  59
  60 #define SECTOR_SHIFT            9
  61 #define SECTOR_SIZE             (1 << SECTOR_SHIFT)
  62 #define SECTORS_PER_PAGE_SHIFT  (PAGE_SHIFT - SECTOR_SHIFT)
  63 #define SECTORS_PER_PAGE        (1 << SECTORS_PER_PAGE_SHIFT)
  64 #define ZRAM_LOGICAL_BLOCK_SHIFT 12
  65 #define ZRAM_LOGICAL_BLOCK_SIZE (1 << ZRAM_LOGICAL_BLOCK_SHIFT)
  66 #define ZRAM_SECTOR_PER_LOGICAL_BLOCK   \
  67         (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
  68
  69 /* Flags for zram pages (table[page_no].flags) */
  70 enum zram_pageflags {
  71         /* Page is stored uncompressed */
  72         ZRAM_UNCOMPRESSED,
  73
  74         /* Page consists entirely of zeros */
  75         ZRAM_ZERO,
  76
  77         __NR_ZRAM_PAGEFLAGS,
  78 };
  79
  80 /*-- Data structures */
  81
  82 /* Allocated for each disk page */
  83 struct table {
  84         struct page *page;
  85         u16 offset;
  86         u8 count;       /* object ref count (not yet used) */
  87         u8 flags;
  88 } __attribute__((aligned(4)));
  89
  90 struct zram_stats {
  91         u64 compr_size;         /* compressed size of pages stored */
  92         u64 num_reads;          /* failed + successful */
  93         u64 num_writes;         /* --do-- */
  94         u64 failed_reads;       /* should NEVER! happen */
  95         u64 failed_writes;      /* can happen when memory is too low */
  96         u64 invalid_io;         /* non-page-aligned I/O requests */
  97         u64 notify_free;        /* no. of swap slot free notifications */
  98         u32 pages_zero;         /* no. of zero filled pages */
  99         u32 pages_stored;       /* no. of pages currently stored */
 100         u32 good_compress;      /* % of pages with compression ratio<=50% */
 101         u32 pages_expand;       /* % of incompressible pages */
 102 };
 103
 104 struct zram {
 105         struct xv_pool *mem_pool;
 106         void *compress_workmem;
 107         void *compress_buffer;
 108         struct table *table;
 109         spinlock_t stat64_lock; /* protect 64-bit stats */
 110         struct rw_semaphore lock; /* protect compression buffers and table
 111                                    * against concurrent read and writes */
 112         struct request_queue *queue;
 113         struct gendisk *disk;
 114         int init_done;
 115         /* Prevent concurrent execution of device init and reset */
 116         struct mutex init_lock;
 117         /*
 118          * This is the limit on amount of *uncompressed* worth of data
 119          * we can store in a disk.
 120          */
 121         u64 disksize;   /* bytes */
 122
 123         struct zram_stats stats;
 124 };
 125
 126 extern struct zram *devices;
 127 extern unsigned int num_devices;
 128 #ifdef CONFIG_SYSFS
 129 extern struct attribute_group zram_disk_attr_group;
 130 #endif
 131
 132 extern int zram_init_device(struct zram *zram);
 133 extern void zram_reset_device(struct zram *zram);
 134
 135 #endif