Documentation/accounting/delay-accounting.rst: add thrashing page cache and direct compact

Add thrashing page cache and direct compact related descriptions and
update the usage of getdelays userspace utility.

The following patches modifications have been updated:
https://lore.kernel.org/all/20190312102002.31737-4-jinpuwang@gmail.com/
https://lore.kernel.org/all/1638619795-71451-1-git-send-email-
wang.yong12@zte.com.cn/

Link: https://lkml.kernel.org/r/1639583021-92977-1-git-send-email-wang.yong12@zte.com.cn
Signed-off-by: wangyong <wang.yong12@zte.com.cn>
Reviewed-by: Yang Yang <yang.yang29@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: wangyong

Documentation/accounting/delay-accounting.rst

@@ -13,6 +13,8 @@ a) waiting for a CPU (while being runnable)
 b) completion of synchronous block I/O initiated by the task
 c) swapping in pages
 d) memory reclaim
+e) thrashing page cache
+f) direct compact
 
 and makes these statistics available to userspace through
 the taskstats interface.
@@ -41,11 +43,12 @@ generic data structure to userspace corresponding to per-pid and per-tgid
 statistics. The delay accounting functionality populates specific fields of
 this structure. See
 
-     include/linux/taskstats.h
+     include/uapi/linux/taskstats.h
 
 for a description of the fields pertaining to delay accounting.
 It will generally be in the form of counters returning the cumulative
-delay seen for cpu, sync block I/O, swapin, memory reclaim etc.
+delay seen for cpu, sync block I/O, swapin, memory reclaim, thrash page
+cache, direct compact etc.
 
 Taking the difference of two successive readings of a given
 counter (say cpu_delay_total) for a task will give the delay
@@ -88,41 +91,37 @@ seen.
 
 General format of the getdelays command::
 
-	getdelays [-t tgid] [-p pid] [-c cmd...]
-
+	getdelays [-dilv] [-t tgid] [-p pid]
 
 Get delays, since system boot, for pid 10::
 
-	# ./getdelays -p 10
+	# ./getdelays -d -p 10
 	(output similar to next case)
 
 Get sum of delays, since system boot, for all pids with tgid 5::
 
-	# ./getdelays -t 5
-
-
-	CPU	count	real total	virtual total	delay total
-		7876	92005750	100000000	24001500
-	IO	count	delay total
-		0	0
-	SWAP	count	delay total
-		0	0
-	RECLAIM	count	delay total
-		0	0
+	# ./getdelays -d -t 5
+	print delayacct stats ON
+	TGID	5
 
-Get delays seen in executing a given simple command::
 
-  # ./getdelays -c ls /
+	CPU             count     real total  virtual total    delay total  delay average
+	                    8        7000000        6872122        3382277          0.423ms
+	IO              count    delay total  delay average
+		            0              0              0ms
+	SWAP            count    delay total  delay average
+	                    0              0              0ms
+	RECLAIM         count    delay total  delay average
+		            0              0              0ms
+	THRASHING       count    delay total  delay average
+	                    0              0              0ms
+	COMPACT         count    delay total  delay average
+	                    0              0              0ms
 
-  bin   data1  data3  data5  dev  home  media  opt   root  srv        sys  usr
-  boot  data2  data4  data6  etc  lib   mnt    proc  sbin  subdomain  tmp  var
+Get IO accounting for pid 1, it works only with -p::
 
+	# ./getdelays -i -p 1
+	printing IO accounting
+	linuxrc: read=65536, write=0, cancelled_write=0
 
-  CPU	count	real total	virtual total	delay total
-	6	4000250		4000000		0
-  IO	count	delay total
-	0	0
-  SWAP	count	delay total
-	0	0
-  RECLAIM	count	delay total
-	0	0
+The above command can be used with -v to get more debug information.