This creates RAM based block device (called ramzswap0) which is used as swap disk.

On write (swap-out):
- compress page (using LZO)
- Allocate required amount of memory (using TLSF)
- Store reference to its location in simple array.

On read (swap-in):
- Get compressed page location from array
- Decompress this page.

Signed-off-by: Nitin Gupta
---
drivers/block/Kconfig | 27 +++
drivers/block/Makefile | 1 +
drivers/block/compcache.c | 432 +++++++++++++++++++++++++++++++++++++++++++++
drivers/block/compcache.h | 95 ++++++++++
4 files changed, 555 insertions(+), 0 deletions(-)

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 0d1d213..d4ed9da 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -347,6 +347,33 @@ config BLK_DEV_RAM_SIZE
The default value is 4096 kilobytes. Only change this if you know
what you are doing.

+config BLK_DEV_COMPCACHE
+ tristate "Compressed RAM based swap device"
+ select TLSF
+ select LZO_COMPRESS
+ select LZO_DECOMPRESS
+ help
+ This creates RAM based block device which acts as swap disk. Pages
+ swapped to this disk are compressed and stored in memory itself.
+ Project Home: http://code.google.com/p/compcache/
+
+config BLK_DEV_COMPCACHE_DEBUG
+ default y
+ depends on BLK_DEV_COMPCACHE
+ bool "Enable debugging"
+ help
+ This causes negligible performance loss and size increase.
+ If unsure, say Y.
+
+config BLK_DEV_COMPCACHE_STATS
+ default y
+ depends on BLK_DEV_COMPCACHE
+ bool "Enable statistics"
+ help
+ Creates /proc/compcache to export various statistics.
+ This adds about 4K to size with negligible performance loss.
+ If unsure, say Y.
+
config BLK_DEV_XIP
bool "Support XIP filesystems on RAM block device"
depends on BLK_DEV_RAM
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index 5e58430..b6d3dd2 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -12,6 +12,7 @@ obj-$(CONFIG_PS3_DISK) += ps3disk.o
obj-$(CONFIG_ATARI_FLOPPY) += ataflop.o
obj-$(CONFIG_AMIGA_Z2RAM) += z2ram.o
obj-$(CONFIG_BLK_DEV_RAM) += brd.o
+obj-$(CONFIG_BLK_DEV_COMPCACHE) += compcache.o
obj-$(CONFIG_BLK_DEV_LOOP) += loop.o
obj-$(CONFIG_BLK_DEV_XD) += xd.o
obj-$(CONFIG_BLK_CPQ_DA) += cpqarray.o
diff --git a/drivers/block/compcache.c b/drivers/block/compcache.c
new file mode 100644
index 0000000..b413cdd
--- /dev/null
+++ b/drivers/block/compcache.c
@@ -0,0 +1,432 @@
+/*
+ * Compressed RAM based swap device
+ *
+ * (C) 2008 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 the GNU General Public
+ * License (version 2). See linux/COPYING for more information.
+ *
+ * Project home: http://code.google.com/p/compcache
+ */
+
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+
+#include "compcache.h"
+
+static struct block_device_operations compcache_devops = {
+ .owner = THIS_MODULE,
+};
+
+static struct compcache compcache;
+static unsigned long compcache_size_kbytes;
+#if defined(STATS)
+static struct compcache_stats stats;
+#endif
+
+#if defined(STATS)
+static struct proc_dir_entry *proc;
+
+static int proc_compcache_read(char *page, char **start, off_t off,
+ int count, int *eof, void *data)
+{
+ int len;
+#if defined(STATS)
+ size_t succ_writes;
+ unsigned int good_compress_perc = 0, no_compress_perc = 0;
+#endif
+
+ if (off > 0) {
+ *eof = 1;
+ return 0;
+ }
+
+ len = sprintf(page,
+ "DiskSize: %8zu kB\n",
+ compcache.size >> (10 - SECTOR_SHIFT));
+#if defined(STATS)
+ succ_writes = stats.num_writes - stats.failed_writes;
+ if (succ_writes) {
+ good_compress_perc = stats.good_compress * 100 / succ_writes;
+ no_compress_perc = stats.pages_expand * 100 / succ_writes;
+ }
+
+#define K(x) ((x) >> 10)
+ len += sprintf(page + len,
+ "NumReads: %8u\n"
+ "NumWrites: %8u\n"
+ "FailedReads: %8u\n"
+ "FailedWrites: %8u\n"
+ "InvalidIO: %8u\n"
+ "GoodCompress: %8u %%\n"
+ "NoCompress: %8u %%\n"
+ "CurrentPages: %8zu\n"
+ "CurrentMem: %8zu kB\n"
+ "PeakMem: %8zu kB\n",
+ stats.num_reads,
+ stats.num_writes,
+ stats.failed_reads,
+ stats.failed_writes,
+ stats.invalid_io,
+ good_compress_perc,
+ no_compress_perc,
+ stats.curr_pages,
+ K(stats.curr_mem),
+ K(stats.peak_mem));
+#endif
+ return len;
+}
+#endif /* STATS */
+
+/* Check if request is within bounds and page aligned */
+static inline int valid_swap_request(struct bio *bio)
+{
+ if (unlikely((bio->bi_sector >= compcache.size) ||
+ (bio->bi_sector & (SECTORS_PER_PAGE - 1)) ||
+ (bio->bi_vcnt != 1) ||
+ (bio->bi_size != PAGE_SIZE) ||
+ (bio->bi_io_vec[0].bv_offset != 0)))
+ return 0;
+ return 1;
+}
+
+static int compcache_make_request(struct request_queue *queue, struct bio *bio)
+{
+ int ret;
+ size_t clen, page_no;
+ void *user_mem;
+ struct page *page;
+
+ if (!valid_swap_request(bio)) {
+ stat_inc(stats.invalid_io);
+ goto out_nomap;
+ }
+
+ page = bio->bi_io_vec[0].bv_page;
+ page_no = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
+ user_mem = kmap(page);
+
+ if (bio_data_dir(bio) == READ) {
+ stat_inc(stats.num_reads);
+ /*
+ * This is attempt to read before any previous write
+ * to this location. This happens due to readahead when
+ * swap device is read from user-space (e.g. during swapon)
+ */
+ if (unlikely(compcache.table[page_no].addr == NULL)) {
+ pr_debug("Read before write on swap device: "
+ "sector=%lu, size=%u, offset=%u\n",
+ (ulong)(bio->bi_sector),
+ bio->bi_size,
+ bio->bi_io_vec[0].bv_offset);
+ memset(user_mem, 0, PAGE_SIZE);
+ kunmap(page);
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+ bio_endio(bio, 0);
+ return 0;
+ }
+
+ /* Page is stored uncompressed since its incompressible */
+ if (unlikely(compcache.table[page_no].len == PAGE_SIZE)) {
+ memcpy(user_mem, compcache.table[page_no].addr,
+ PAGE_SIZE);
+ kunmap(page);
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+ bio_endio(bio, 0);
+ return 0;
+ }
+
+ clen = PAGE_SIZE;
+ ret = lzo1x_decompress_safe(
+ compcache.table[page_no].addr,
+ compcache.table[page_no].len,
+ user_mem,
+ &clen);
+
+ /* should NEVER happen */
+ if (unlikely(ret != LZO_E_OK)) {
+ pr_err(C "Decompression failed! "
+ "err=%d, page=%zu, len=%lu\n", ret, page_no,
+ compcache.table[page_no].len);
+ stat_inc(stats.failed_reads);
+ goto out;
+ }
+
+ kunmap(page);
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+ bio_endio(bio, 0);
+ return 0;
+ } else { /* Write */
+ unsigned char *src = compcache.compress_buffer;
+ stat_inc(stats.num_writes);
+ /*
+ * System swaps to same sector again when the stored page
+ * is no longer referenced by any process. So, its now safe
+ * to free the memory that was allocated for this page.
+ */
+ if (compcache.table[page_no].addr) {
+ tlsf_free(compcache.table[page_no].addr,
+ compcache.mem_pool);
+ stat_dec(stats.curr_pages);
+ stat_set(stats.curr_mem, stats.curr_mem -
+ compcache.table[page_no].len);
+ compcache.table[page_no].addr = NULL;
+ compcache.table[page_no].len = 0;
+ }
+
+ mutex_lock(&compcache.lock);
+ ret = lzo1x_1_compress(user_mem, PAGE_SIZE,
+ src, &clen, compcache.compress_workmem);
+ if (unlikely(ret != LZO_E_OK)) {
+ mutex_unlock(&compcache.lock);
+ pr_err(C "Compression failed! err=%d\n", ret);
+ compcache.table[page_no].addr = NULL;
+ compcache.table[page_no].len = 0;
+ stat_inc(stats.failed_writes);
+ goto out;
+ }
+
+ /* Page is incompressible - store it as is */
+ if (clen >= PAGE_SIZE) {
+ pr_debug("Page expand on compression: "
+ "page=%zu, size=%zu\n", page_no, clen);
+ clen = PAGE_SIZE;
+ src = user_mem;
+ }
+
+ if ((compcache.table[page_no].addr = tlsf_malloc(clen,
+ compcache.mem_pool)) == NULL) {
+ mutex_unlock(&compcache.lock);
+ pr_err(C "Error allocating memory for compressed "
+ "page: %zu, size=%zu \n", page_no, clen);
+ compcache.table[page_no].len = 0;
+ stat_inc(stats.failed_writes);
+ goto out;
+ }
+
+ memcpy(compcache.table[page_no].addr, src, clen);
+
+ /* Update stats */
+ stat_inc(stats.curr_pages);
+ stat_set(stats.curr_mem, stats.curr_mem + clen);
+ stat_setmax(stats.peak_mem, stats.curr_mem);
+ stat_inc_if_less(stats.pages_expand, PAGE_SIZE - 1, clen);
+ stat_inc_if_less(stats.good_compress, clen,
+ PAGE_SIZE / 2 + 1);
+ mutex_unlock(&compcache.lock);
+
+ compcache.table[page_no].len = clen;
+
+ kunmap(page);
+ set_bit(BIO_UPTODATE, &bio->bi_flags);
+ bio_endio(bio, 0);
+ return 0;
+ }
+out:
+ kunmap(page);
+out_nomap:
+ bio_io_error(bio);
+ return 0;
+}
+
+static void setup_swap_header(union swap_header *s)
+{
+ s->info.version = 1;
+ s->info.last_page = compcache.size >> SECTORS_PER_PAGE_SHIFT;
+ s->info.nr_badpages = 0;
+ memcpy(s->magic.magic, "SWAPSPACE2", 10);
+}
+
+static void *get_mem(size_t size)
+{
+ return __vmalloc(size, GFP_NOIO, PAGE_KERNEL);
+}
+
+static void put_mem(void *ptr)
+{
+ vfree(ptr);
+}
+
+static int __init compcache_init(void)
+{
+ int ret;
+ size_t num_pages;
+ struct sysinfo i;
+
+ mutex_init(&compcache.lock);
+
+ if (compcache_size_kbytes == 0) {
+ pr_info(C "compcache size not provided."
+ " Using default: (%u%% of Total RAM).\n"
+ "Use compcache_size_kbytes module param to specify"
+ " custom size\n", DEFAULT_COMPCACHE_PERCENT);
+ si_meminfo(&i);
+ compcache_size_kbytes = ((DEFAULT_COMPCACHE_PERCENT *
+ i.totalram) / 100) << (PAGE_SHIFT - 10);
+ }
+
+ compcache.size = compcache_size_kbytes << 10;
+ compcache.size = (compcache.size + PAGE_SIZE - 1) & PAGE_MASK;
+ pr_info(C "Compressed swap size set to: %zu KB\n", compcache.size >> 10);
+ compcache.size >>= SECTOR_SHIFT;
+
+ compcache.compress_workmem = kmalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
+ if (compcache.compress_workmem == NULL) {
+ pr_err(C "Error allocating compressor working memory\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ compcache.compress_buffer = kmalloc(2 * PAGE_SIZE, GFP_KERNEL);
+ if (compcache.compress_buffer == NULL) {
+ pr_err(C "Error allocating compressor buffer space\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ num_pages = compcache.size >> SECTORS_PER_PAGE_SHIFT;
+ compcache.table = vmalloc(num_pages * sizeof(*compcache.table));
+ if (compcache.table == NULL) {
+ pr_err(C "Error allocating compcache address table\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+ memset(compcache.table, 0, num_pages * sizeof(*compcache.table));
+
+ compcache.table[0].addr = (void *)get_zeroed_page(GFP_KERNEL);
+ if (compcache.table[0].addr == NULL) {
+ pr_err(C "Error allocating swap header page\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+ compcache.table[0].len = PAGE_SIZE;
+ setup_swap_header((union swap_header *)(compcache.table[0].addr));
+
+ compcache.disk = alloc_disk(1);
+ if (compcache.disk == NULL) {
+ pr_err(C "Error allocating disk structure\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ compcache.disk->first_minor = 0;
+ compcache.disk->fops = &compcache_devops;
+ /*
+ * It is named like this to prevent distro installers
+ * from offering compcache as installation target. They
+ * seem to ignore all devices beginning with 'ram'
+ */
+ strcpy(compcache.disk->disk_name, "ramzswap0");
+
+ compcache.disk->major = register_blkdev(0, compcache.disk->disk_name);
+ if (compcache.disk->major < 0) {
+ pr_err(C "Cannot register block device\n");
+ ret = -EFAULT;
+ goto fail;
+ }
+
+ compcache.disk->queue = blk_alloc_queue(GFP_KERNEL);
+ if (compcache.disk->queue == NULL) {
+ pr_err(C "Cannot register disk queue\n");
+ ret = -EFAULT;
+ goto fail;
+ }
+
+ set_capacity(compcache.disk, compcache.size);
+ blk_queue_make_request(compcache.disk->queue, compcache_make_request);
+ blk_queue_hardsect_size(compcache.disk->queue, PAGE_SIZE);
+ add_disk(compcache.disk);
+
+ compcache.mem_pool = tlsf_create_memory_pool("compcache",
+ get_mem, put_mem,
+ INIT_SIZE_BYTES, 0, GROW_SIZE_BYTES);
+ if (compcache.mem_pool == NULL) {
+ pr_err(C "Error creating memory pool\n");
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+#if defined(STATS)
+ proc = create_proc_entry("compcache", S_IRUGO, NULL);
+ if (proc)
+ proc->read_proc = &proc_compcache_read;
+ else {
+ ret = -ENOMEM;
+ pr_warning(C "Error creating proc entry\n");
+ goto fail;
+ }
+#endif
+
+ pr_debug(C "Initialization done!\n");
+ return 0;
+
+fail:
+ if (compcache.disk != NULL) {
+ if (compcache.disk->major > 0)
+ unregister_blkdev(compcache.disk->major,
+ compcache.disk->disk_name);
+ del_gendisk(compcache.disk);
+ }
+
+ free_page((unsigned long)compcache.table[0].addr);
+ kfree(compcache.compress_workmem);
+ kfree(compcache.compress_buffer);
+ vfree(compcache.table);
+ tlsf_destroy_memory_pool(compcache.mem_pool);
+#if defined(STATS)
+ if (proc)
+ remove_proc_entry("compcache", &proc_root);
+#endif
+ pr_err(C "Initialization failed: err=%d\n", ret);
+ return ret;
+}
+
+static void __exit compcache_exit(void)
+{
+ size_t i, num_pages;
+ num_pages = compcache.size >> SECTORS_PER_PAGE_SHIFT;
+
+ unregister_blkdev(compcache.disk->major, compcache.disk->disk_name);
+ del_gendisk(compcache.disk);
+ free_page((unsigned long)compcache.table[0].addr);
+ kfree(compcache.compress_workmem);
+ kfree(compcache.compress_buffer);
+
+ /* Free all pages that are still in compcache */
+ for (i = 1; i < num_pages; i++)
+ if (compcache.table[i].addr)
+ tlsf_free(compcache.table[i].addr, compcache.mem_pool);
+ vfree(compcache.table);
+ tlsf_destroy_memory_pool(compcache.mem_pool);
+
+#if defined(STATS)
+ remove_proc_entry("compcache", &proc_root);
+#endif
+ pr_debug("cleanup done!\n");
+}
+
+module_param(compcache_size_kbytes, ulong, 0);
+MODULE_PARM_DESC(compcache_size_kbytes, "compcache device size (in KB)");
+
+module_init(compcache_init);
+module_exit(compcache_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nitin Gupta ");
+MODULE_DESCRIPTION("Compressed RAM Based Swap Device");
diff --git a/drivers/block/compcache.h b/drivers/block/compcache.h
new file mode 100644
index 0000000..5b57f57
--- /dev/null
+++ b/drivers/block/compcache.h
@@ -0,0 +1,95 @@
+/*
+ * Compressed RAM based swap device
+ *
+ * (C) 2008 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 the GNU General Public
+ * License (version 2). See linux/COPYING for more information.
+ *
+ * Project home: http://code.google.com/p/compcache
+ */
+
+#ifndef _COMPCACHE_H_
+#define _COMPCACHE_H_
+
+#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)
+
+/*-- Configurable parameters */
+/* Default compcache size: 25% of total RAM */
+#define DEFAULT_COMPCACHE_PERCENT 25
+#define INIT_SIZE_BYTES (16 * 1024)
+#define GROW_SIZE_BYTES INIT_SIZE_BYTES
+/*-- */
+
+/* Message prefix */
+#define C "compcache: "
+
+/* Debugging and Stats */
+#define NOP do { } while(0)
+
+#if defined(CONFIG_BLK_DEV_COMPCACHE_DEBUG)
+#define DEBUG
+#endif
+
+#if defined(CONFIG_BLK_DEV_COMPCACHE_STATS)
+#define STATS
+#endif
+
+#if defined(STATS)
+#define stat_inc(stat) (stat++)
+#define stat_dec(stat) (stat--)
+#define stat_set(stat, val) (stat = val)
+#define stat_setmax(stat, curr) (stat = (curr) > stat ? (curr) : stat)
+#define stat_inc_if_less(stat, val1, val2) \
+ (stat += ((val1) < (val2) ? 1 : 0))
+#else /* STATS */
+#define stat_inc(x) NOP
+#define stat_dec(x) NOP
+#define stat_set(x, v) NOP
+#define stat_setmax(x, v) NOP
+#define stat_inc_if_less(x, v1, v2) NOP
+#endif /* STATS */
+
+/*-- Data structures */
+/* Indexed by page no. */
+struct table {
+ void *addr;
+ unsigned long len;
+};
+
+struct compcache {
+ void *mem_pool;
+ void *compress_workmem;
+ void *compress_buffer;
+ struct table *table;
+ struct mutex lock;
+ struct gendisk *disk;
+ size_t size; /* In sectors */
+};
+
+#if defined(STATS)
+struct compcache_stats {
+ u32 num_reads; /* failed + successful */
+ u32 num_writes; /* --do-- */
+ u32 failed_reads; /* can happen when memory is tooo low */
+ u32 failed_writes; /* should NEVER! happen */
+ u32 invalid_io; /* non-swap I/O requests */
+ u32 good_compress; /* no. of pages with compression
+ * ratio <= 50%. TODO: export full
+ * compressed page size histogram */
+ u32 pages_expand; /* no. of incompressible pages */
+ size_t curr_pages; /* current no. of compressed pages */
+ size_t curr_mem; /* current total size of compressed pages */
+ size_t peak_mem;
+};
+#endif
+/*-- */
+
+#endif
--
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