linux_dsm_epyc7002/Documentation/ABI/testing/sysfs-block-zram
Minchan Kim 1d69a3f8ae zram: idle writeback fixes and cleanup
This patch includes some fixes and cleanup for idle-page writeback.

1. writeback_limit interface

Now writeback_limit interface is rather conusing.  For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment.  IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.

To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable

* before:
  while true :
    # to re-enable writeback limit once previous one is used up
    echo 0 > /sys/block/zram0/writeback_limit
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

* new
  # To enable writeback limit, from the beginning, admin should
  # enable it.
  echo $((200<<20)) > /sys/block/zram0/writeback_limit
  echo 1 > /sys/block/zram/0/writeback_limit_enable
  while true :
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

It's much strightforward.

2. fix condition check idle/huge writeback mode check

The mode in writeback_store is not bit opeartion any more so no need to
use bit operations.  Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.

3. clean up idle_store

No need to use goto.

[minchan@kernel.org: missed spin_lock_init]
  Link: http://lkml.kernel.org/r/20190103001601.GA255139@google.com
Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Suggested-by: John Dias <joaodias@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: John Dias <joaodias@google.com>
Cc: Srinivas Paladugu <srnvs@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-01-08 17:15:10 -08:00

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What: /sys/block/zram<id>/disksize
Date: August 2010
Contact: Nitin Gupta <ngupta@vflare.org>
Description:
The disksize file is read-write and specifies the disk size
which represents the limit on the *uncompressed* worth of data
that can be stored in this disk.
Unit: bytes
What: /sys/block/zram<id>/initstate
Date: August 2010
Contact: Nitin Gupta <ngupta@vflare.org>
Description:
The initstate file is read-only and shows the initialization
state of the device.
What: /sys/block/zram<id>/reset
Date: August 2010
Contact: Nitin Gupta <ngupta@vflare.org>
Description:
The reset file is write-only and allows resetting the
device. The reset operation frees all the memory associated
with this device.
What: /sys/block/zram<id>/max_comp_streams
Date: February 2014
Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Description:
The max_comp_streams file is read-write and specifies the
number of backend's zcomp_strm compression streams (number of
concurrent compress operations).
What: /sys/block/zram<id>/comp_algorithm
Date: February 2014
Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Description:
The comp_algorithm file is read-write and lets to show
available and selected compression algorithms, change
compression algorithm selection.
What: /sys/block/zram<id>/mem_used_max
Date: August 2014
Contact: Minchan Kim <minchan@kernel.org>
Description:
The mem_used_max file is write-only and is used to reset
the counter 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
What: /sys/block/zram<id>/mem_limit
Date: August 2014
Contact: Minchan Kim <minchan@kernel.org>
Description:
The mem_limit file is write-only 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
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.
What: /sys/block/zram<id>/io_stat
Date: August 2015
Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Description:
The io_stat file is read-only and accumulates device's I/O
statistics not accounted by block layer. For example,
failed_reads, failed_writes, etc. File format is similar to
block layer statistics file format.
What: /sys/block/zram<id>/mm_stat
Date: August 2015
Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Description:
The mm_stat file is read-only and represents device's mm
statistics (orig_data_size, compr_data_size, etc.) in a format
similar to block layer statistics file format.
What: /sys/block/zram<id>/debug_stat
Date: July 2016
Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Description:
The debug_stat file is read-only and represents various
device's debugging info useful for kernel developers. Its
format is not documented intentionally and may change
anytime without any notice.
What: /sys/block/zram<id>/backing_dev
Date: June 2017
Contact: Minchan Kim <minchan@kernel.org>
Description:
The backing_dev file is read-write and set up backing
device for zram to write incompressible pages.
For using, user should enable CONFIG_ZRAM_WRITEBACK.
What: /sys/block/zram<id>/idle
Date: November 2018
Contact: Minchan Kim <minchan@kernel.org>
Description:
idle file is write-only and mark zram slot as idle.
If system has mounted debugfs, user can see which slots
are idle via /sys/kernel/debug/zram/zram<id>/block_state
What: /sys/block/zram<id>/writeback
Date: November 2018
Contact: Minchan Kim <minchan@kernel.org>
Description:
The writeback file is write-only and trigger idle and/or
huge page writeback to backing device.
What: /sys/block/zram<id>/bd_stat
Date: November 2018
Contact: Minchan Kim <minchan@kernel.org>
Description:
The bd_stat file is read-only and represents backing device's
statistics (bd_count, bd_reads, bd_writes) in a format
similar to block layer statistics file format.
What: /sys/block/zram<id>/writeback_limit_enable
Date: November 2018
Contact: Minchan Kim <minchan@kernel.org>
Description:
The writeback_limit_enable file is read-write and specifies
eanbe of writeback_limit feature. "1" means eable the feature.
No limit "0" is the initial state.
What: /sys/block/zram<id>/writeback_limit
Date: November 2018
Contact: Minchan Kim <minchan@kernel.org>
Description:
The writeback_limit file is read-write and specifies the maximum
amount of writeback ZRAM can do. The limit could be changed
in run time.