zram_drv.h

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/*
 * Compressed RAM block device
 *
 * Copyright (C) 2008, 2009, 2010  Nitin Gupta
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the licence that better fits your requirements.
 *
 * Released under the terms of 3-clause BSD License
 * Released under the terms of GNU General Public License Version 2.0
 *
 * Project home: http://compcache.googlecode.com
 */

#ifndef _ZRAM_DRV_H_
#define _ZRAM_DRV_H_

#include <linux/spinlock.h>
#include <linux/mutex.h>

#include "../zsmalloc/zsmalloc.h"

/*
 * Some arbitrary value. This is just to catch
 * invalid value for num_devices module parameter.
 */
static const unsigned max_num_devices = 32;

/*-- Configurable parameters */

/* Default zram disk size: 25% of total RAM */
static const unsigned default_disksize_perc_ram = 25;

/*
 * Pages that compress to size greater than this are stored
 * uncompressed in memory.
 */
static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;

/*
 * NOTE: max_zpage_size must be less than or equal to:
 *   ZS_MAX_ALLOC_SIZE - sizeof(struct zobj_header)
 * otherwise, xv_malloc() would always return failure.
 */

/*-- End of configurable params */

#define SECTOR_SHIFT        9
#define SECTOR_SIZE     (1 << SECTOR_SHIFT)
#define SECTORS_PER_PAGE_SHIFT  (PAGE_SHIFT - SECTOR_SHIFT)
#define SECTORS_PER_PAGE    (1 << SECTORS_PER_PAGE_SHIFT)
#define ZRAM_LOGICAL_BLOCK_SHIFT 12
#define ZRAM_LOGICAL_BLOCK_SIZE (1 << ZRAM_LOGICAL_BLOCK_SHIFT)
#define ZRAM_SECTOR_PER_LOGICAL_BLOCK   \
    (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))

/* Flags for zram pages (table[page_no].flags) */
enum zram_pageflags {
    /* Page consists entirely of zeros */
    ZRAM_ZERO,

    __NR_ZRAM_PAGEFLAGS,
};

/*-- Data structures */

/* Allocated for each disk page */
struct table {
    unsigned long handle;
    u16 size;   /* object size (excluding header) */
    u8 count;   /* object ref count (not yet used) */
    u8 flags;
} __aligned(4);

struct zram_stats {
    u64 compr_size;     /* compressed size of pages stored */
    u64 num_reads;      /* failed + successful */
    u64 num_writes;     /* --do-- */
    u64 failed_reads;   /* should NEVER! happen */
    u64 failed_writes;  /* can happen when memory is too low */
    u64 invalid_io;     /* non-page-aligned I/O requests */
    u64 notify_free;    /* no. of swap slot free notifications */
    u32 pages_zero;     /* no. of zero filled pages */
    u32 pages_stored;   /* no. of pages currently stored */
    u32 good_compress;  /* % of pages with compression ratio<=50% */
    u32 bad_compress;   /* % of pages with compression ratio>=75% */
};

struct zram {
    struct zs_pool *mem_pool;
    void *compress_workmem;
    void *compress_buffer;
    struct table *table;
    spinlock_t stat64_lock; /* protect 64-bit stats */
    struct rw_semaphore lock; /* protect compression buffers and table
                   * against concurrent read and writes */
    struct request_queue *queue;
    struct gendisk *disk;
    int init_done;
    /* Prevent concurrent execution of device init, reset and R/W request */
    struct rw_semaphore init_lock;
    /*
     * This is the limit on amount of *uncompressed* worth of data
     * we can store in a disk.
     */
    u64 disksize;   /* bytes */

    struct zram_stats stats;
};

extern struct zram *zram_devices;
unsigned int zram_get_num_devices(void);
#ifdef CONFIG_SYSFS
extern struct attribute_group zram_disk_attr_group;
#endif

extern int zram_init_device(struct zram *zram);
extern void __zram_reset_device(struct zram *zram);

#endif