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/*
* Compressed RAM based swap device
*
* Copyright (C) 2008, 2009 Nitin Gupta
*
* This RAM based block device acts as swap disk.
* Pages swapped to this device are compressed and
* stored in memory.
*
* Released under the terms of GNU General Public License Version 2.0
*
* Project home: http://compcache.googlecode.com
*/
#ifndef _RAMZSWAP_H_
#define _RAMZSWAP_H_
#include "xvmalloc.h"
/*
* Stored at beginning of each compressed object.
*
* It stores back-reference to table entry which points to this
* object. This is required to support memory defragmentation or
* migrating compressed pages to backing swap disk.
*/
struct zobj_header {
#if 0
u32 table_idx;
#endif
};
/*-- Configurable parameters */
/* Default ramzswap disk size: 25% of total RAM */
#define DEFAULT_DISKSIZE_PERC_RAM 25
#define DEFAULT_MEMLIMIT_PERC_RAM 15
/*
* Max compressed page size when backing device is provided.
* Pages that compress to size greater than this are sent to
* physical swap disk.
*/
#define MAX_CPAGE_SIZE_BDEV (PAGE_SIZE / 2)
/*
* Max compressed page size when there is no backing dev.
* Pages that compress to size greater than this are stored
* uncompressed in memory.
*/
#define MAX_CPAGE_SIZE_NOBDEV (PAGE_SIZE / 4 * 3)
/*
* NOTE: MAX_CPAGE_SIZE_{BDEV,NOBDEV} sizes must be
* less than or equal to:
* XV_MAX_ALLOC_SIZE - sizeof(struct zobj_header)
* since otherwise xvMalloc 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)
/* Message prefix */
#define C "ramzswap: "
/* Debugging and Stats */
#define NOP do { } while (0)
#if defined(CONFIG_BLK_DEV_RAMZSWAP_STATS)
#define STATS
#endif
#if defined(STATS)
#define stat_inc(stat) ((stat)++)
#define stat_dec(stat) ((stat)--)
#define stat_inc_if_less(stat, val1, val2) \
((stat) += ((val1) < (val2) ? 1 : 0))
#define stat_dec_if_less(stat, val1, val2) \
((stat) -= ((val1) < (val2) ? 1 : 0))
#else /* STATS */
#define stat_inc(x) NOP
#define stat_dec(x) NOP
#define stat_inc_if_less(x, v1, v2) NOP
#define stat_dec_if_less(x, v1, v2) NOP
#endif /* STATS */
/* Flags for ramzswap pages (table[page_no].flags) */
enum rzs_pageflags {
/* Page is stored uncompressed */
RZS_UNCOMPRESSED,
/* Page consists entirely of zeros */
RZS_ZERO,
__NR_RZS_PAGEFLAGS,
};
/*-- Data structures */
/* Indexed by page no. */
struct table {
u32 pagenum;
u16 offset;
u8 count; /* object ref count (not yet used) */
u8 flags;
};
struct ramzswap {
struct xv_pool *mem_pool;
void *compress_workmem;
void *compress_buffer;
struct table *table;
struct mutex lock;
struct gendisk *disk;
/*
* This is limit on compressed data size (stats.compr_size)
* Its applicable only when backing swap device is present.
*/
size_t memlimit; /* bytes */
/*
* This is limit on amount of *uncompressed* worth of data
* we can hold. When backing swap device is provided, it is
* set equal to device size.
*/
size_t disksize; /* bytes */
/* backing swap device info */
struct block_device *backing_swap;
struct file *swap_file;
int old_block_size;
};
struct ramzswap_stats {
/* basic stats */
size_t compr_size; /* compressed size of pages stored -
* needed to enforce memlimit */
/* more stats */
#if defined(STATS)
u64 num_reads; /* failed + successful */
u64 num_writes; /* --do-- */
u64 failed_reads; /* can happen when memory is too low */
u64 failed_writes; /* should NEVER! happen */
u64 invalid_io; /* non-swap I/O requests */
u64 pages_discard; /* no. of pages freed by discard callback */
u32 pages_zero; /* no. of zero filled pages */
u32 pages_stored; /* no. of pages currently stored */
u32 good_compress; /* no. of pages with compression ratio<=50% */
u32 pages_expand; /* no. of incompressible pages */
u64 bdev_num_reads; /* no. of reads on backing dev */
u64 bdev_num_writes; /* no. of writes on backing dev */
#endif
};
/*-- */
#endif
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