LXR linux/drivers/staging/zram/zram

   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 */
  27static 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 */
  35struct 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 */
  44static 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 */
  50static 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_SIZE 4096
  65
  66/* Flags for zram pages (table[page_no].flags) */
  67enum zram_pageflags {
  68        /* Page is stored uncompressed */
  69        ZRAM_UNCOMPRESSED,
  70
  71        /* Page consists entirely of zeros */
  72        ZRAM_ZERO,
  73
  74        __NR_ZRAM_PAGEFLAGS,
  75};
  76
  77/*-- Data structures */
  78
  79/* Allocated for each disk page */
  80struct table {
  81        struct page *page;
  82        u16 offset;
  83        u8 count;       /* object ref count (not yet used) */
  84        u8 flags;
  85} __attribute__((aligned(4)));
  86
  87struct zram_stats {
  88        u64 compr_size;         /* compressed size of pages stored */
  89        u64 num_reads;          /* failed + successful */
  90        u64 num_writes;         /* --do-- */
  91        u64 failed_reads;       /* should NEVER! happen */
  92        u64 failed_writes;      /* can happen when memory is too low */
  93        u64 invalid_io;         /* non-page-aligned I/O requests */
  94        u64 notify_free;        /* no. of swap slot free notifications */
  95        u32 pages_zero;         /* no. of zero filled pages */
  96        u32 pages_stored;       /* no. of pages currently stored */
  97        u32 good_compress;      /* % of pages with compression ratio<=50% */
  98        u32 pages_expand;       /* % of incompressible pages */
  99};
 100
 101struct zram {
 102        struct xv_pool *mem_pool;
 103        void *compress_workmem;
 104        void *compress_buffer;
 105        struct table *table;
 106        spinlock_t stat64_lock; /* protect 64-bit stats */
 107        struct mutex lock;      /* protect compression buffers against
 108                                 * concurrent writes */
 109        struct request_queue *queue;
 110        struct gendisk *disk;
 111        int init_done;
 112        /* Prevent concurrent execution of device init and reset */
 113        struct mutex init_lock;
 114        /*
 115         * This is the limit on amount of *uncompressed* worth of data
 116         * we can store in a disk.
 117         */
 118        u64 disksize;   /* bytes */
 119
 120        struct zram_stats stats;
 121};
 122
 123extern struct zram *devices;
 124extern unsigned int num_devices;
 125#ifdef CONFIG_SYSFS
 126extern struct attribute_group zram_disk_attr_group;
 127#endif
 128
 129extern int zram_init_device(struct zram *zram);
 130extern void zram_reset_device(struct zram *zram);
 131
 132#endif
 133