[lineage-18.1] Update

Documentation/ABI/testing/sysfs-block-zram

@@ -22,41 +22,6 @@ Description:
 		device. The reset operation frees all the memory associated
 		with this device.
 
-What:		/sys/block/zram<id>/num_reads
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-Description:
-		The num_reads file is read-only and specifies the number of
-		reads (failed or successful) done on this device.
-
-What:		/sys/block/zram<id>/num_writes
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-Description:
-		The num_writes file is read-only and specifies the number of
-		writes (failed or successful) done on this device.
-
-What:		/sys/block/zram<id>/invalid_io
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-Description:
-		The invalid_io file is read-only and specifies the number of
-		non-page-size-aligned I/O requests issued to this device.
-
-What:		/sys/block/zram<id>/failed_reads
-Date:		February 2014
-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.
-
-What:		/sys/block/zram<id>/failed_writes
-Date:		February 2014
-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.
-
 What:		/sys/block/zram<id>/max_comp_streams
 Date:		February 2014
 Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
@@ -73,74 +38,24 @@ Description:
 		available and selected compression algorithms, change
 		compression algorithm selection.
 
-What:		/sys/block/zram<id>/notify_free
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-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.
-
-What:		/sys/block/zram<id>/zero_pages
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-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.
-
-What:		/sys/block/zram<id>/orig_data_size
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-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
-
-What:		/sys/block/zram<id>/compr_data_size
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-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
-
-What:		/sys/block/zram<id>/mem_used_total
-Date:		August 2010
-Contact:	Nitin Gupta <ngupta@vflare.org>
-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
-
 What:		/sys/block/zram<id>/mem_used_max
 Date:		August 2014
 Contact:	Minchan Kim <minchan@kernel.org>
 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.
+		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 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
+		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
@@ -166,3 +81,20 @@ 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.

Documentation/blockdev/zram.txt

@@ -59,62 +59,72 @@ num_devices parameter is optional and tells zram how many devices should be
 pre-created. Default: 1.
 
 2) Set max number of compression streams
-	Regardless the value passed to this attribute, ZRAM will always
-	allocate multiple compression streams - one per online CPUs - thus
-	allowing several concurrent compression operations. The number of
-	allocated compression streams goes down when some of the CPUs
-	become offline. There is no single-compression-stream mode anymore,
-	unless you are running a UP system or has only 1 CPU online.
-
-	To find out how many streams are currently available:
+Regardless the value passed to this attribute, ZRAM will always
+allocate multiple compression streams - one per online CPUs - thus
+allowing several concurrent compression operations. The number of
+allocated compression streams goes down when some of the CPUs
+become offline. There is no single-compression-stream mode anymore,
+unless you are running a UP system or has only 1 CPU online.
+
+To find out how many streams are currently available:
 	cat /sys/block/zram0/max_comp_streams
 
 3) Select compression algorithm
-	Using comp_algorithm device attribute one can see available and
-	currently selected (shown in square brackets) compression algorithms,
-	change selected compression algorithm (once the device is initialised
-	there is no way to change compression algorithm).
+Using comp_algorithm device attribute one can see available and
+currently selected (shown in square brackets) compression algorithms,
+change selected compression algorithm (once the device is initialised
+there is no way to change compression algorithm).
 
-	Examples:
+Examples:
 	#show supported compression algorithms
 	cat /sys/block/zram0/comp_algorithm
 	lzo [lz4]
 
 	#select lzo compression algorithm
 	echo lzo > /sys/block/zram0/comp_algorithm
 
+For the time being, the `comp_algorithm' content does not necessarily
+show every compression algorithm supported by the kernel. We keep this
+list primarily to simplify device configuration and one can configure
+a new device with a compression algorithm that is not listed in
+`comp_algorithm'. The thing is that, internally, ZRAM uses Crypto API
+and, if some of the algorithms were built as modules, it's impossible
+to list all of them using, for instance, /proc/crypto or any other
+method. This, however, has an advantage of permitting the usage of
+custom crypto compression modules (implementing S/W or H/W compression).
+
 4) Set Disksize
-        Set disk size by writing the value to sysfs node 'disksize'.
-        The value can be either in bytes or you can use mem suffixes.
-        Examples:
-            # Initialize /dev/zram0 with 50MB disksize
-            echo $((50*1024*1024)) > /sys/block/zram0/disksize
+Set disk size by writing the value to sysfs node 'disksize'.
+The value can be either in bytes or you can use mem suffixes.
+Examples:
+	# Initialize /dev/zram0 with 50MB disksize
+	echo $((50*1024*1024)) > /sys/block/zram0/disksize
 
-            # Using mem suffixes
-            echo 256K > /sys/block/zram0/disksize
-            echo 512M > /sys/block/zram0/disksize
-            echo 1G > /sys/block/zram0/disksize
+	# Using mem suffixes
+	echo 256K > /sys/block/zram0/disksize
+	echo 512M > /sys/block/zram0/disksize
+	echo 1G > /sys/block/zram0/disksize
 
 Note:
 There is little point creating a zram of greater than twice the size of memory
 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
 size of the disk when not in use so a huge zram is wasteful.
 
 5) Set memory limit: Optional
-	Set memory limit by writing the value to sysfs node 'mem_limit'.
-	The value can be either in bytes or you can use mem suffixes.
-	In addition, you could change the value in runtime.
-	Examples:
-	    # limit /dev/zram0 with 50MB memory
-	    echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
+Set memory limit by writing the value to sysfs node 'mem_limit'.
+The value can be either in bytes or you can use mem suffixes.
+In addition, you could change the value in runtime.
+Examples:
+	# limit /dev/zram0 with 50MB memory
+	echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
 
-	    # Using mem suffixes
-	    echo 256K > /sys/block/zram0/mem_limit
-	    echo 512M > /sys/block/zram0/mem_limit
-	    echo 1G > /sys/block/zram0/mem_limit
+	# Using mem suffixes
+	echo 256K > /sys/block/zram0/mem_limit
+	echo 512M > /sys/block/zram0/mem_limit
+	echo 1G > /sys/block/zram0/mem_limit
 
-	    # To disable memory limit
-	    echo 0 > /sys/block/zram0/mem_limit
+	# To disable memory limit
+	echo 0 > /sys/block/zram0/mem_limit
 
 6) Activate:
 	mkswap /dev/zram0
@@ -151,41 +161,15 @@ Name            access            description
 disksize          RW    show and set the device's disk size
 initstate         RO    shows the initialization state of the device
 reset             WO    trigger device reset
-num_reads         RO    the number of reads
-failed_reads      RO    the number of failed reads
-num_write         RO    the number of writes
-failed_writes     RO    the number of failed writes
-invalid_io        RO    the number of non-page-size-aligned I/O requests
+mem_used_max      WO    reset the `mem_used_max' counter (see later)
+mem_limit         WO    specifies the maximum amount of memory ZRAM can use
+                        to store the compressed data
 max_comp_streams  RW    the number of possible concurrent compress operations
 comp_algorithm    RW    show and change the compression algorithm
-notify_free       RO    the number of notifications to free pages (either
-                        slot free notifications or REQ_DISCARD requests)
-zero_pages        RO    the number of zero filled pages written to this disk
-orig_data_size    RO    uncompressed size of data stored in this disk
-compr_data_size   RO    compressed size of data stored in this disk
-mem_used_total    RO    the amount of memory allocated for this disk
-mem_used_max      RW    the maximum amount of memory zram have consumed to
-                        store the data (to reset this counter to the actual
-                        current value, write 1 to this attribute)
-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
+debug_stat        RO    this file is used for zram debugging purposes
+backing_dev	  RW	set up backend storage for zram to write out
 
-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.
 
@@ -200,22 +184,41 @@ The stat file represents device's I/O statistics not accounted by block
 layer and, thus, not available in zram<id>/stat file. It consists of a
 single line of text and contains the following stats separated by
 whitespace:
-	failed_reads
-	failed_writes
-	invalid_io
-	notify_free
+ failed_reads     the number of failed reads
+ failed_writes    the number of failed writes
+ invalid_io       the number of non-page-size-aligned I/O requests
+ notify_free      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.
 
 File /sys/block/zram<id>/mm_stat
 
 The stat file represents device's mm statistics. It consists of a single
 line of text and contains the following stats separated by whitespace:
-	orig_data_size
-	compr_data_size
-	mem_used_total
-	mem_limit
-	mem_used_max
-	zero_pages
-	num_migrated
+ orig_data_size   uncompressed size of data stored in this disk.
+		  This excludes same-element-filled pages (same_pages) since
+		  no memory is allocated for them.
+                  Unit: bytes
+ compr_data_size  compressed size of data stored in this disk
+ mem_used_total   the amount of memory allocated for this disk. This
+                  includes 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
+ mem_limit        the maximum amount of memory ZRAM can use to store
+                  the compressed data
+ mem_used_max     the maximum amount of memory zram have consumed to
+                  store the data
+ same_pages       the number of same element filled pages written to this disk.
+                  No memory is allocated for such pages.
+ pages_compacted  the number of pages freed during compaction
+ huge_pages	  the number of incompressible pages
 
 9) Deactivate:
 	swapoff /dev/zram0
@@ -230,5 +233,39 @@ line of text and contains the following stats separated by whitespace:
 	resets the disksize to zero. You must set the disksize again
 	before reusing the device.
 
+* Optional Feature
+
+= writeback
+
+With incompressible pages, there is no memory saving with zram.
+Instead, with CONFIG_ZRAM_WRITEBACK, zram can write incompressible page
+to backing storage rather than keeping it in memory.
+User should set up backing device via /sys/block/zramX/backing_dev
+before disksize setting.
+
+= memory tracking
+
+With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
+zram block. It could be useful to catch cold or incompressible
+pages of the process with*pagemap.
+If you enable the feature, you could see block state via
+/sys/kernel/debug/zram/zram0/block_state". The output is as follows,
+
+	  300    75.033841 .wh
+	  301    63.806904 s..
+	  302    63.806919 ..h
+
+First column is zram's block index.
+Second column is access time since the system was booted
+Third column is state of the block.
+(s: same page
+w: written page to backing store
+h: huge page)
+
+First line of above example says 300th block is accessed at 75.033841sec
+and the block's state is huge so it is written back to the backing
+storage. It's a debugging feature so anyone shouldn't rely on it to work
+properly.
+
 Nitin Gupta
 ngupta@vflare.org