zram: compare all the entries with same checksum for deduplication

Until now, we compare just one entry with same checksum when
checking duplication since it is the simplest way to implement.
However, for the completeness, checking all the entries is better
so this patch implement to compare all the entries with same checksum.
Since this event would be rare so there would be no performance loss.

Change-Id: Ie7d61c14d127a28f5a06d85b0ca66b9fada20cbb
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: https://lore.kernel.org/patchwork/patch/787163/
Patch-mainline: linux-kernel@ Thu, 11 May 2017 22:30:29
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
Signed-off-by: Marco Zanin <mrczn.bb@gmail.com>
Signed-off-by: snnbyyds <snnbyyds@gmail.com>

Author: JoonsooKim

drivers/block/zram/zram_dedup.c

@@ -109,6 +109,51 @@ static unsigned long zram_dedup_put(struct zram *zram,
 	return entry->refcount;
 }
 
+static struct zram_entry *__zram_dedup_get(struct zram *zram,
+				struct zram_hash *hash, unsigned char *mem,
+				struct zram_entry *entry)
+{
+	struct zram_entry *tmp, *prev = NULL;
+	struct rb_node *rb_node;
+
+	/* find left-most entry with same checksum */
+	while ((rb_node = rb_prev(&entry->rb_node))) {
+		tmp = rb_entry(rb_node, struct zram_entry, rb_node);
+		if (tmp->checksum != entry->checksum)
+			break;
+
+		entry = tmp;
+	}
+
+again:
+	entry->refcount++;
+	atomic64_add(entry->len, &zram->stats.dup_data_size);
+	spin_unlock(&hash->lock);
+
+	if (prev)
+		zram_entry_free(zram, prev);
+
+	if (zram_dedup_match(zram, entry, mem))
+		return entry;
+
+	spin_lock(&hash->lock);
+	tmp = NULL;
+	rb_node = rb_next(&entry->rb_node);
+	if (rb_node)
+		tmp = rb_entry(rb_node, struct zram_entry, rb_node);
+
+	if (tmp && (tmp->checksum == entry->checksum)) {
+		prev = entry;
+		entry = tmp;
+		goto again;
+	}
+
+	spin_unlock(&hash->lock);
+	zram_entry_free(zram, entry);
+
+	return NULL;
+}
+
 static struct zram_entry *zram_dedup_get(struct zram *zram,
 				unsigned char *mem, u32 checksum)
 {
@@ -122,18 +167,8 @@ static struct zram_entry *zram_dedup_get(struct zram *zram,
 	rb_node = hash->rb_root.rb_node;
 	while (rb_node) {
 		entry = rb_entry(rb_node, struct zram_entry, rb_node);
-		if (checksum == entry->checksum) {
-			entry->refcount++;
-			atomic64_add(entry->len, &zram->stats.dup_data_size);
-			spin_unlock(&hash->lock);
-
-			if (zram_dedup_match(zram, entry, mem))
-				return entry;
-
-			zram_entry_free(zram, entry);
-
-			return NULL;
-		}
+		if (checksum == entry->checksum)
+			return __zram_dedup_get(zram, hash, mem, entry);
 
 		if (checksum < entry->checksum)
 			rb_node = rb_node->rb_left;