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

Minchan Kim
2015-03-12T23:56:02Z

Hi Sergey,

On Thu, Mar 12, 2015 at 11:47:18PM +0900, Sergey Senozhatsky wrote:
> 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);

How about adding pid, comm? Admin can know which process touches.

> +}
> +
> #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)); \

It just reports once for first-touched stat and miss other stats by ZRAM_ATTR_RO.
Of course, you warned "See zram documentation" so he might know about other stats
plan, too. If it's your intention, let's make warn more clear.

"Atrribute $s will be removed. Also, there are other stats we will remove
in future. See Documentation/blockdev/zram.txt"

> 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
>

--
Kind regards,
Minchan Kim