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 "../zsmalloc/zsmalloc.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 /*-- Configurable parameters */
  30
  31 /*
  32  * Pages that compress to size greater than this are stored
  33  * uncompressed in memory.
  34  */
  35 static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
  36
  37 /*
  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.
  41  */
  42
  43 /*-- End of configurable params */
  44
  45 #define SECTOR_SHIFT            9
  46 #define SECTOR_SIZE             (1 << SECTOR_SHIFT)
  47 #define SECTORS_PER_PAGE_SHIFT  (PAGE_SHIFT - SECTOR_SHIFT)
  48 #define SECTORS_PER_PAGE        (1 << SECTORS_PER_PAGE_SHIFT)
  49 #define ZRAM_LOGICAL_BLOCK_SHIFT 12
  50 #define ZRAM_LOGICAL_BLOCK_SIZE (1 << ZRAM_LOGICAL_BLOCK_SHIFT)
  51 #define ZRAM_SECTOR_PER_LOGICAL_BLOCK   \
  52         (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
  53
  54 /* Flags for zram pages (table[page_no].flags) */
  55 enum zram_pageflags {
  56         /* Page consists entirely of zeros */
  57         ZRAM_ZERO,
  58
  59         __NR_ZRAM_PAGEFLAGS,
  60 };
  61
  62 /*-- Data structures */
  63
  64 /* Allocated for each disk page */
  65 struct table {
  66         unsigned long handle;
  67         u16 size;       /* object size (excluding header) */
  68         u8 count;       /* object ref count (not yet used) */
  69         u8 flags;
  70 } __aligned(4);
  71
  72 /*
  73  * All 64bit fields should only be manipulated by 64bit atomic accessors.
  74  * All modifications to 32bit counter should be protected by zram->lock.
  75  */
  76 struct zram_stats {
  77         atomic64_t compr_size;  /* compressed size of pages stored */
  78         atomic64_t num_reads;   /* failed + successful */
  79         atomic64_t num_writes;  /* --do-- */
  80         atomic64_t failed_reads;        /* should NEVER! happen */
  81         atomic64_t failed_writes;       /* can happen when memory is too low */
  82         atomic64_t invalid_io;  /* non-page-aligned I/O requests */
  83         atomic64_t notify_free; /* no. of swap slot free notifications */
  84         u32 pages_zero;         /* no. of zero filled pages */
  85         u32 pages_stored;       /* no. of pages currently stored */
  86         u32 good_compress;      /* % of pages with compression ratio<=50% */
  87         u32 bad_compress;       /* % of pages with compression ratio>=75% */
  88 };
  89
  90 struct zram_meta {
  91         void *compress_workmem;
  92         void *compress_buffer;
  93         struct table *table;
  94         struct zs_pool *mem_pool;
  95 };
  96
  97 struct zram {
  98         struct zram_meta *meta;
  99         struct rw_semaphore lock; /* protect compression buffers, table,
 100                                    * 32bit stat counters against concurrent
 101                                    * notifications, reads and writes */
 102         struct request_queue *queue;
 103         struct gendisk *disk;
 104         int init_done;
 105         /* Prevent concurrent execution of device init, reset and R/W request */
 106         struct rw_semaphore init_lock;
 107         /*
 108          * This is the limit on amount of *uncompressed* worth of data
 109          * we can store in a disk.
 110          */
 111         u64 disksize;   /* bytes */
 112
 113         struct zram_stats stats;
 114 };
 115 #endif