zram: switch to 64-bit hash for dedup

The original dedup code does not handle collision from the observation
that it practically does not happen.

For additional peace of mind, use a bigger hash size for reducing the
possibility of collision even further.

Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Change-Id: I4543ce22d69a21b2edcc72a72790d2c55a9e312c

drivers/block/zram/zram_dedup.c

@@ -28,13 +28,13 @@ u64 zram_dedup_meta_size(struct zram *zram)
 	return (u64)atomic64_read(&zram->stats.meta_data_size);
 }
 
-static u32 zram_dedup_checksum(unsigned char *mem)
+static u64 zram_dedup_checksum(unsigned char *mem)
 {
-	return xxhash(mem, PAGE_SIZE, 0);
+	return xxh64(mem, PAGE_SIZE, 0);
 }
 
 void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
-				u32 checksum)
+				u64 checksum)
 {
 	struct zram_hash *hash;
 	struct rb_root *rb_root;
@@ -91,7 +91,7 @@ static unsigned long zram_dedup_put(struct zram *zram,
 				struct zram_entry *entry)
 {
 	struct zram_hash *hash;
-	u32 checksum;
+	u64 checksum;
 	unsigned long val;
 
 	checksum = entry->checksum;
@@ -156,7 +156,7 @@ again:
 }
 
 static struct zram_entry *zram_dedup_get(struct zram *zram,
-				unsigned char *mem, u32 checksum)
+				unsigned char *mem, u64 checksum)
 {
 	struct zram_hash *hash;
 	struct zram_entry *entry;
@@ -182,7 +182,7 @@ static struct zram_entry *zram_dedup_get(struct zram *zram,
 }
 
 struct zram_entry *zram_dedup_find(struct zram *zram, struct page *page,
-				u32 *checksum)
+				u64 *checksum)
 {
 	void *mem;
 	struct zram_entry *entry;

drivers/block/zram/zram_dedup.h

@@ -10,9 +10,9 @@ u64 zram_dedup_dup_size(struct zram *zram);
 u64 zram_dedup_meta_size(struct zram *zram);
 
 void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
-				u32 checksum);
+				u64 checksum);
 struct zram_entry *zram_dedup_find(struct zram *zram, struct page *page,
-				u32 *checksum);
+				u64 *checksum);
 
 void zram_dedup_init_entry(struct zram *zram, struct zram_entry *entry,
 				unsigned long handle, unsigned int len);
@@ -26,9 +26,9 @@ static inline u64 zram_dedup_dup_size(struct zram *zram) { return 0; }
 static inline u64 zram_dedup_meta_size(struct zram *zram) { return 0; }
 
 static inline void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
-			u32 checksum) { }
+			u64 checksum) { }
 static inline struct zram_entry *zram_dedup_find(struct zram *zram,
-			struct page *page, u32 *checksum) { return NULL; }
+			struct page *page, u64 *checksum) { return NULL; }
 
 static inline void zram_dedup_init_entry(struct zram *zram,
 			struct zram_entry *entry, unsigned long handle,

drivers/block/zram/zram_drv.c

@@ -3093,7 +3093,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	void *src, *dst, *mem;
 	struct zcomp_strm *zstrm;
 	struct page *page = bvec->bv_page;
-	u32 checksum;
+	u64 checksum;
 	unsigned long element = 0;
 	enum zram_pageflags flags = 0;
 #ifdef CONFIG_ZRAM_LRU_WRITEBACK

drivers/block/zram/zram_drv.h

@@ -68,7 +68,7 @@ enum zram_pageflags {
 struct zram_entry {
 	struct rb_node rb_node;
 	u32 len;
-	u32 checksum;
+	u64 checksum;
 	unsigned long refcount;
 	unsigned long handle;
 };