[PATCH 2/3] zram: make compact a read-write sysfs node

Sergey Senozhatsky
2015-07-11T09:46:37Z

Change zram's `compact' sysfs node to be a read-write attribute.
Write triggers zsmalloc compaction, just as before, read returns
the number of pages that zsmalloc can potentially compact.

User space now has a chance to estimate possible compaction memory
savings and avoid unnecessary compactions.

Example:

if [ `cat /sys/block/zram<id>/compact` -gt 10 ]; then
echo 1 > /sys/block/zram<id>/compact;
fi

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
Documentation/ABI/testing/sysfs-block-zram | 7 ++++---
Documentation/blockdev/zram.txt | 4 +++-
drivers/block/zram/zram_drv.c | 16 +++++++++++++++-
3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 2e69e83..0093998 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -146,9 +146,10 @@ What: /sys/block/zram<id>/compact
Date: August 2015
Contact: Minchan Kim <minchan@kernel.org>
Description:
- The compact file is write-only and trigger compaction for
- allocator zrm uses. The allocator moves some objects so that
- it could free fragment space.
+ The compact file is read/write. Write triggers underlying
+ allocator's memory compaction, which may result in memory
+ savings. Read returns the number of pages that compaction
+ can potentially (but not guaranteed to) free.

What: /sys/block/zram<id>/io_stat
Date: August 2015
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 62435bb..1854f62 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -146,7 +146,9 @@ mem_limit RW the maximum amount of memory ZRAM can use to store
the compressed data
pages_compacted RO the number of pages freed during compaction
(available only via zram<id>/mm_stat node)
-compact WO trigger memory compaction
+compact RW write triggers memory compaction, read shows how many
+ pages can potentially (but not necessarily will) be
+ compacted

WARNING
=======
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f5ef9e0..def9b8a 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -404,6 +404,20 @@ static ssize_t compact_store(struct device *dev,
return len;
}

+static ssize_t compact_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct zram *zram = dev_to_zram(dev);
+ unsigned long num_pages = 0;
+
+ down_read(&zram->init_lock);
+ if (init_done(zram))
+ num_pages = zs_pages_to_compact(zram->meta->mem_pool);
+ up_read(&zram->init_lock);
+
+ return scnprintf(buf, PAGE_SIZE, "%lu\n", num_pages);
+}
+
static ssize_t io_stat_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
@@ -1145,7 +1159,7 @@ static const struct block_device_operations zram_devops = {
.owner = THIS_MODULE
};

-static DEVICE_ATTR_WO(compact);
+static DEVICE_ATTR_RW(compact);
static DEVICE_ATTR_RW(disksize);
static DEVICE_ATTR_RO(initstate);
static DEVICE_ATTR_WO(reset);
--
2.4.5