[PATCHv2 7/7] zram: deprecate zram attrs sysfs nodes

Sergey Senozhatsky
2015-03-12T14:47:34Z

Add Documentation/ABI/obsolete/sysfs-block-zram file and list
obsolete and deprecated attributes there. The patch also adds
additional information to zram documentation and describes the
basic strategy:
- the existing RW nodes will be downgraded to WO nodes (in 4.11)
- deprecated RO sysfs nodes will eventually be removed (in 4.11)

Users will be additionally notified about deprecated attr usage
by pr_warn_once() (added to every deprecated attr _show()), as
suggested by Minchan Kim.

Example:
zram: Attribute mem_used_max will be removed. See zram documentation.

User space is advised to use zram<id>/stat, zram<id>/io_stat and
zram<id>/mm_stat files.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
Documentation/ABI/obsolete/sysfs-block-zram | 119 ++++++++++++++++++++++++++++
Documentation/blockdev/zram.txt | 16 ++++
drivers/block/zram/zram_drv.c | 12 +++
3 files changed, 147 insertions(+)
create mode 100644 Documentation/ABI/obsolete/sysfs-block-zram

diff --git a/Documentation/ABI/obsolete/sysfs-block-zram b/Documentation/ABI/obsolete/sysfs-block-zram
new file mode 100644
index 0000000..720ea92
--- /dev/null
+++ b/Documentation/ABI/obsolete/sysfs-block-zram
@@ -0,0 +1,119 @@
+What: /sys/block/zram<id>/num_reads
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The num_reads file is read-only and specifies the number of
+ reads (failed or successful) done on this device.
+ Now accessible via zram<id>/stat node.
+
+What: /sys/block/zram<id>/num_writes
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The num_writes file is read-only and specifies the number of
+ writes (failed or successful) done on this device.
+ Now accessible via zram<id>/stat node.
+
+What: /sys/block/zram<id>/invalid_io
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The invalid_io file is read-only and specifies the number of
+ non-page-size-aligned I/O requests issued to this device.
+ Now accessible via zram<id>/io_stat node.
+
+What: /sys/block/zram<id>/failed_reads
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The failed_reads file is read-only and specifies the number of
+ failed reads happened on this device.
+ Now accessible via zram<id>/io_stat node.
+
+What: /sys/block/zram<id>/failed_writes
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The failed_writes file is read-only and specifies the number of
+ failed writes happened on this device.
+ Now accessible via zram<id>/io_stat node.
+
+What: /sys/block/zram<id>/notify_free
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The notify_free file is read-only. Depending on device usage
+ scenario it may account a) the number of pages freed because
+ of swap slot free notifications or b) the number of pages freed
+ because of REQ_DISCARD requests sent by bio. The former ones
+ are sent to a swap block device when a swap slot is freed, which
+ implies that this disk is being used as a swap disk. The latter
+ ones are sent by filesystem mounted with discard option,
+ whenever some data blocks are getting discarded.
+ Now accessible via zram<id>/io_stat node.
+
+What: /sys/block/zram<id>/zero_pages
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The zero_pages file is read-only and specifies number of zero
+ filled pages written to this disk. No memory is allocated for
+ such pages.
+ Now accessible via zram<id>/mm_stat node.
+
+What: /sys/block/zram<id>/orig_data_size
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The orig_data_size file is read-only and specifies uncompressed
+ size of data stored in this disk. This excludes zero-filled
+ pages (zero_pages) since no memory is allocated for them.
+ Unit: bytes
+ Now accessible via zram<id>/mm_stat node.
+
+What: /sys/block/zram<id>/compr_data_size
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The compr_data_size file is read-only and specifies compressed
+ size of data stored in this disk. So, compression ratio can be
+ calculated using orig_data_size and this statistic.
+ Unit: bytes
+ Now accessible via zram<id>/mm_stat node.
+
+What: /sys/block/zram<id>/mem_used_total
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The mem_used_total file is read-only and specifies the amount
+ of memory, including allocator fragmentation and metadata
+ overhead, allocated for this disk. So, allocator space
+ efficiency can be calculated using compr_data_size and this
+ statistic.
+ Unit: bytes
+ Now accessible via zram<id>/mm_stat node.
+
+What: /sys/block/zram<id>/mem_used_max
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The mem_used_max file is read/write and specifies the amount
+ of maximum memory zram have consumed to store compressed data.
+ For resetting the value, you should write "0". Otherwise,
+ you could see -EINVAL.
+ Unit: bytes
+ Downgraded to write-only node: so it's possible to set new
+ value only; its current value is stored in zram<id>/mm_stat
+ node.
+
+What: /sys/block/zram<id>/mem_limit
+Date: August 2015
+Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+ The mem_limit file is read/write and specifies the maximum
+ amount of memory ZRAM can use to store the compressed data.
+ The limit could be changed in run time and "0" means disable
+ the limit. No limit is the initial state. Unit: bytes
+ Downgraded to write-only node: so it's possible to set new
+ value only; its current value is stored in zram<id>/mm_stat
+ node.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index b133138..44b1a77 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -148,6 +148,22 @@ num_migrated RO the number of objects migrated migrated by compaction
compact WO trigger memory compaction

+WARNING
+=======
+per-stat sysfs attributes are considered to be deprecated.
+The basic strategy is:
+-- the existing RW nodes will be downgraded to WO nodes (in linux 4.11)
+-- deprecated RO sysfs nodes will eventually be removed (in linux 4.11)
+
+The list of deprecated attributes can be found here:
+Documentation/ABI/obsolete/sysfs-block-zram
+
+Basically, every attribute that has its own read accessible sysfs node
+(e.g. num_reads) *AND* is accessible via one of the stat files (zram<id>/stat
+or zram<id>/io_stat or zram<id>/mm_stat) is considered to be deprecated.
+
+User space is advised to use the following files to read the device statistics.
+
File /sys/block/zram<id>/stat

Represents block layer statistics. Read Documentation/block/stat.txt for
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7493096..2aced91 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -47,11 +47,19 @@ static const char *default_compressor = "lzo";
/* Module params (documentation at end) */
static unsigned int num_devices = 1;

+static inline void deprecated_attr_warn(const char *name)
+{
+ pr_warn_once("Attribute %s will be removed. See zram documentation.\n",
+ name);
+}
+
#define ZRAM_ATTR_RO(name) \
static ssize_t name##_show(struct device *d, \
struct device_attribute *attr, char *b) \
{ \
struct zram *zram = dev_to_zram(d); \
+ \
+ deprecated_attr_warn(__stringify(name)); \
return scnprintf(b, PAGE_SIZE, "%llu\n", \
(u64)atomic64_read(&zram->stats.name)); \
} \
@@ -206,6 +214,7 @@ static ssize_t orig_data_size_show(struct device *dev,
{
struct zram *zram = dev_to_zram(dev);

+ deprecated_attr_warn("orig_data_size");
return scnprintf(buf, PAGE_SIZE, "%llu\n",
(u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT);
}
@@ -216,6 +225,7 @@ static ssize_t mem_used_total_show(struct device *dev,
u64 val = 0;
struct zram *zram = dev_to_zram(dev);

+ deprecated_attr_warn("mem_used_total");
down_read(&zram->init_lock);
if (init_done(zram)) {
struct zram_meta *meta = zram->meta;
@@ -245,6 +255,7 @@ static ssize_t mem_limit_show(struct device *dev,
u64 val;
struct zram *zram = dev_to_zram(dev);

+ deprecated_attr_warn("mem_limit");
down_read(&zram->init_lock);
val = zram->limit_pages;
up_read(&zram->init_lock);
@@ -276,6 +287,7 @@ static ssize_t mem_used_max_show(struct device *dev,
u64 val = 0;
struct zram *zram = dev_to_zram(dev);

+ deprecated_attr_warn("mem_used_max");
down_read(&zram->init_lock);
if (init_done(zram))
val = atomic_long_read(&zram->stats.max_used_pages);
--
2.3.2.209.gd67f9d5