[PATCH] zram: enable compaction support in zram

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

Commit c72c6160d967 ("zram: move compact_store() to sysfs functions area")
was intended to be a cosmetic change that moved function around w/o any
functional change:
http://lkml.iu.edu/hypermail/linux/kernel/1503.1/01818.html

Unfortunately, on its way from mmotm to Linus's tree it was altered and turned
into "remove compaction support from zram" commit. I've managed to create a
mess of commits and Andrew had to pick some of the commits and hand edit them.

Fix it and learn my lessons.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 Documentation/blockdev/zram.txt |  2 +-
 drivers/block/zram/zram_drv.c   | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 48a183e..bef4998 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -126,7 +126,7 @@ mem_used_max      RW    the maximum amount memory zram have consumed to
 mem_limit         RW    the maximum amount of memory ZRAM can use to store
                         the compressed data
 num_migrated      RO    the number of objects migrated migrated by compaction
-
+compact           WO    trigger memory compaction
 
 WARNING
 =======
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index c94386a..f474cbe 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -261,6 +261,27 @@ static ssize_t comp_algorithm_store(struct device *dev,
 	return len;
 }
 
+static ssize_t compact_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	unsigned long nr_migrated;
+	struct zram *zram = dev_to_zram(dev);
+	struct zram_meta *meta;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		up_read(&zram->init_lock);
+		return -EINVAL;
+	}
+
+	meta = zram->meta;
+	nr_migrated = zs_compact(meta->mem_pool);
+	atomic64_add(nr_migrated, &zram->stats.num_migrated);
+	up_read(&zram->init_lock);
+
+	return len;
+}
+
 /* flag operations needs meta->tb_lock */
 static int zram_test_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
@@ -1038,6 +1059,7 @@ static const struct block_device_operations zram_devops = {
 	.owner = THIS_MODULE
 };
 
+static DEVICE_ATTR_WO(compact);
 static DEVICE_ATTR_RW(disksize);
 static DEVICE_ATTR_RO(initstate);
 static DEVICE_ATTR_WO(reset);
@@ -1114,6 +1136,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_num_writes.attr,
 	&dev_attr_failed_reads.attr,
 	&dev_attr_failed_writes.attr,
+	&dev_attr_compact.attr,
 	&dev_attr_invalid_io.attr,
 	&dev_attr_notify_free.attr,
 	&dev_attr_zero_pages.attr,
-- 
2.4.0.rc1.29.gecc46a1