updated to patched ZRAM (thanks to @faux123)

kernel/arch/arm/configs/uckernel_defconfig

@@ -1990,7 +1990,14 @@ CONFIG_ANDROID_LOW_MEMORY_KILLER=y
 # RAR Register Driver
 #
 # CONFIG_IIO is not set
+CONFIG_XVMALLOC=y
 CONFIG_ZRAM=y
+CONFIG_ZRAM_NUM_DEVICES=1
+CONFIG_ZRAM_DEFAULT_PERCENTAGE=25
+# CONFIG_ZRAM_DEBUG is not set
+CONFIG_ZRAM_LZO=y
+# CONFIG_ZRAM_SNAPPY is not set
+CONFIG_ZRAM_DEFAULT_DISKSIZE=100663296
 # CONFIG_BATMAN_ADV is not set
 # CONFIG_FB_SM7XX is not set
 

kernel/drivers/staging/Makefile

@@ -40,7 +40,8 @@ obj-$(CONFIG_RAR_REGISTER)	+= rar_register/
 obj-$(CONFIG_MRST_RAR_HANDLER)	+= memrar/
 obj-$(CONFIG_DX_SEP)		+= sep/
 obj-$(CONFIG_IIO)		+= iio/
-obj-$(CONFIG_ZRAM)              += zram/
+obj-$(CONFIG_ZRAM)		+= zram/
+obj-$(CONFIG_XVMALLOC)		+= zram/
 obj-$(CONFIG_WLAGS49_H2)	+= wlags49_h2/
 obj-$(CONFIG_WLAGS49_H25)	+= wlags49_h25/
 obj-$(CONFIG_BATMAN_ADV)	+= batman-adv/

kernel/drivers/staging/zram/Kconfig

@@ -1,8 +1,11 @@
+config XVMALLOC
+	bool
+	default n
+
 config ZRAM
 	tristate "Compressed RAM block device support"
-	depends on BLOCK
-	select LZO_COMPRESS
-	select LZO_DECOMPRESS
+	depends on BLOCK && SYSFS
+	select XVMALLOC
 	default n
 	help
 	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
@@ -15,3 +18,54 @@ config ZRAM
 
 	  See zram.txt for more information.
 	  Project home: http://compcache.googlecode.com/
+
+config ZRAM_NUM_DEVICES
+	int "Default number of zram devices"
+	depends on ZRAM
+	range 1 32
+	default 1
+	help
+	  Select default number of zram devices. You can override this value
+	  using 'num_devices' module parameter.
+
+config ZRAM_DEFAULT_PERCENTAGE
+	int "Default number of zram percentage"
+	depends on ZRAM
+	range 10 80
+	default 25
+	help
+	  Select default zram disk size: percentage of total RAM
+
+config ZRAM_DEBUG
+	bool "Compressed RAM block device debug support"
+	depends on ZRAM
+	default n
+	help
+	  This option adds additional debugging code to the compressed
+	  RAM block device driver.
+
+choice ZRAM_COMPRESS
+	prompt "compression method"
+	depends on ZRAM
+	default ZRAM_LZO
+	help
+	  Select the compression method used by zram.
+	  LZO is the default. Snappy compresses a bit worse (around ~2%) but
+	  much (~2x) faster, at least on x86-64.
+config ZRAM_LZO
+	bool "LZO compression"
+	select LZO_COMPRESS
+	select LZO_DECOMPRESS
+config ZRAM_SNAPPY
+	bool "Snappy compression"
+	depends on SNAPPY_COMPRESS
+	depends on SNAPPY_DECOMPRESS
+endchoice
+
+config ZRAM_DEFAULT_DISKSIZE
+	int "Default size of zram in bytes"
+	depends on ZRAM
+	default 100663296
+	help
+	  Set default zram disk size (default ~ 96MB)
+

kernel/drivers/staging/zram/Makefile

@@ -1,3 +1,4 @@
-zram-y	:=	zram_drv.o zram_sysfs.o xvmalloc.o
+zram-y	:=	zram_drv.o zram_sysfs.o
 
 obj-$(CONFIG_ZRAM)	+=	zram.o
+obj-$(CONFIG_XVMALLOC)	+=	xvmalloc.o

kernel/drivers/staging/zram/xvmalloc.c

@@ -10,6 +10,12 @@
  * Released under the terms of GNU General Public License Version 2.0
  */
 
+#ifdef CONFIG_ZRAM_DEBUG
+#define DEBUG
+#endif
+
+#include <linux/module.h>
+#include <linux/kernel.h>
 #include <linux/bitops.h>
 #include <linux/errno.h>
 #include <linux/highmem.h>
@@ -46,7 +52,7 @@ static void clear_flag(struct block_header *block, enum blockflags flag)
 }
 
 /*
- * Given <page, offset> pair, provide a derefrencable pointer.
+ * Given <page, offset> pair, provide a dereferencable pointer.
  * This is called from xv_malloc/xv_free path, so it
  * needs to be fast.
  */
@@ -187,7 +193,7 @@ static void insert_block(struct xv_pool *pool, struct page *page, u32 offset,
 	slindex = get_index_for_insert(block->size);
 	flindex = slindex / BITS_PER_LONG;
 
-	block->link.prev_page = 0;
+	block->link.prev_page = NULL;
 	block->link.prev_offset = 0;
 	block->link.next_page = pool->freelist[slindex].page;
 	block->link.next_offset = pool->freelist[slindex].offset;
@@ -200,61 +206,23 @@ static void insert_block(struct xv_pool *pool, struct page *page, u32 offset,
 		nextblock->link.prev_page = page;
 		nextblock->link.prev_offset = offset;
 		put_ptr_atomic(nextblock, KM_USER1);
+		/* If there was a next page then the free bits are set. */
+		return;
 	}
 
 	__set_bit(slindex % BITS_PER_LONG, &pool->slbitmap[flindex]);
 	__set_bit(flindex, &pool->flbitmap);
 }
 
-/*
- * Remove block from head of freelist. Index 'slindex' identifies the freelist.
- */
-static void remove_block_head(struct xv_pool *pool,
-			struct block_header *block, u32 slindex)
-{
-	struct block_header *tmpblock;
-	u32 flindex = slindex / BITS_PER_LONG;
-
-	pool->freelist[slindex].page = block->link.next_page;
-	pool->freelist[slindex].offset = block->link.next_offset;
-	block->link.prev_page = 0;
-	block->link.prev_offset = 0;
-
-	if (!pool->freelist[slindex].page) {
-		__clear_bit(slindex % BITS_PER_LONG, &pool->slbitmap[flindex]);
-		if (!pool->slbitmap[flindex])
-			__clear_bit(flindex, &pool->flbitmap);
-	} else {
-		/*
-		 * DEBUG ONLY: We need not reinitialize freelist head previous
-		 * pointer to 0 - we never depend on its value. But just for
-		 * sanity, lets do it.
-		 */
-		tmpblock = get_ptr_atomic(pool->freelist[slindex].page,
-				pool->freelist[slindex].offset, KM_USER1);
-		tmpblock->link.prev_page = 0;
-		tmpblock->link.prev_offset = 0;
-		put_ptr_atomic(tmpblock, KM_USER1);
-	}
-}
-
 /*
  * Remove block from freelist. Index 'slindex' identifies the freelist.
  */
 static void remove_block(struct xv_pool *pool, struct page *page, u32 offset,
 			struct block_header *block, u32 slindex)
 {
-	u32 flindex;
+	u32 flindex = slindex / BITS_PER_LONG;
 	struct block_header *tmpblock;
 
-	if (pool->freelist[slindex].page == page
-	   && pool->freelist[slindex].offset == offset) {
-		remove_block_head(pool, block, slindex);
-		return;
-	}
-
-	flindex = slindex / BITS_PER_LONG;
-
 	if (block->link.prev_page) {
 		tmpblock = get_ptr_atomic(block->link.prev_page,
 				block->link.prev_offset, KM_USER1);
@@ -270,6 +238,35 @@ static void remove_block(struct xv_pool *pool, struct page *page, u32 offset,
 		tmpblock->link.prev_offset = block->link.prev_offset;
 		put_ptr_atomic(tmpblock, KM_USER1);
 	}
+
+	/* Is this block is at the head of the freelist? */
+	if (pool->freelist[slindex].page == page
+	   && pool->freelist[slindex].offset == offset) {
+
+		pool->freelist[slindex].page = block->link.next_page;
+		pool->freelist[slindex].offset = block->link.next_offset;
+
+		if (pool->freelist[slindex].page) {
+			struct block_header *tmpblock;
+			tmpblock = get_ptr_atomic(pool->freelist[slindex].page,
+					pool->freelist[slindex].offset,
+					KM_USER1);
+			tmpblock->link.prev_page = NULL;
+			tmpblock->link.prev_offset = 0;
+			put_ptr_atomic(tmpblock, KM_USER1);
+		} else {
+			/* This freelist bucket is empty */
+			__clear_bit(slindex % BITS_PER_LONG,
+				    &pool->slbitmap[flindex]);
+			if (!pool->slbitmap[flindex])
+				__clear_bit(flindex, &pool->flbitmap);
+		}
+	}
+
+	block->link.prev_page = NULL;
+	block->link.prev_offset = 0;
+	block->link.next_page = NULL;
+	block->link.next_offset = 0;
 }
 
 /*
@@ -320,11 +317,13 @@ struct xv_pool *xv_create_pool(void)
 
 	return pool;
 }
+EXPORT_SYMBOL_GPL(xv_create_pool);
 
 void xv_destroy_pool(struct xv_pool *pool)
 {
 	kfree(pool);
 }
+EXPORT_SYMBOL_GPL(xv_destroy_pool);
 
 /**
  * xv_malloc - Allocate block of given size from pool.
@@ -378,7 +377,7 @@ int xv_malloc(struct xv_pool *pool, u32 size, struct page **page,
 
 	block = get_ptr_atomic(*page, *offset, KM_USER0);
 
-	remove_block_head(pool, block, index);
+	remove_block(pool, *page, *offset, block, index);
 
 	/* Split the block if required */
 	tmpoffset = *offset + size + XV_ALIGN;
@@ -413,6 +412,7 @@ int xv_malloc(struct xv_pool *pool, u32 size, struct page **page,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(xv_malloc);
 
 /*
  * Free block identified with <page, offset>
@@ -489,6 +489,7 @@ void xv_free(struct xv_pool *pool, struct page *page, u32 offset)
 	put_ptr_atomic(page_start, KM_USER0);
 	spin_unlock(&pool->lock);
 }
+EXPORT_SYMBOL_GPL(xv_free);
 
 u32 xv_get_object_size(void *obj)
 {
@@ -497,6 +498,7 @@ u32 xv_get_object_size(void *obj)
 	blk = (struct block_header *)((char *)(obj) - XV_ALIGN);
 	return blk->size;
 }
+EXPORT_SYMBOL_GPL(xv_get_object_size);
 
 /*
  * Returns total memory used by allocator (userdata + metadata)
@@ -505,3 +507,4 @@ u64 xv_get_total_size_bytes(struct xv_pool *pool)
 {
 	return pool->total_pages << PAGE_SHIFT;
 }
+EXPORT_SYMBOL_GPL(xv_get_total_size_bytes);

kernel/drivers/staging/zram/xvmalloc_int.h

@@ -19,16 +19,28 @@
 /* User configurable params */
 
 /* Must be power of two */
+#ifdef CONFIG_64BIT
+#define XV_ALIGN_SHIFT 3
+#else
 #define XV_ALIGN_SHIFT	2
+#endif
 #define XV_ALIGN	(1 << XV_ALIGN_SHIFT)
 #define XV_ALIGN_MASK	(XV_ALIGN - 1)
 
 /* This must be greater than sizeof(link_free) */
 #define XV_MIN_ALLOC_SIZE	32
 #define XV_MAX_ALLOC_SIZE	(PAGE_SIZE - XV_ALIGN)
 
-/* Free lists are separated by FL_DELTA bytes */
-#define FL_DELTA_SHIFT	3
+/*
+ * Free lists are separated by FL_DELTA bytes
+ * This value is 3 for 4k pages and 4 for 64k pages, for any
+ * other page size, a conservative (PAGE_SHIFT - 9) is used.
+ */
+#if PAGE_SHIFT == 16
+#define FL_DELTA_SHIFT 4
+#else
+#define FL_DELTA_SHIFT (PAGE_SHIFT - 9)
+#endif
 #define FL_DELTA	(1 << FL_DELTA_SHIFT)
 #define FL_DELTA_MASK	(FL_DELTA - 1)
 #define NUM_FREE_LISTS	((XV_MAX_ALLOC_SIZE - XV_MIN_ALLOC_SIZE) \
@@ -75,12 +87,9 @@ struct block_header {
 struct xv_pool {
 	ulong flbitmap;
 	ulong slbitmap[MAX_FLI];
-	spinlock_t lock;
-
+	u64 total_pages;	/* stats */
 	struct freelist_entry freelist[NUM_FREE_LISTS];
-
-	/* stats */
-	u64 total_pages;
+	spinlock_t lock;
 };
 
 #endif