feat: add limit flag, limit the num of files displayed

README.md

@@ -2,7 +2,7 @@
 
 `pgcacher` is used to get page cache statistics for files. Use the **pgcacher** command to know how much cache space the fd of the specified process occupies in the page cache.  Use **pgcacher** to know whether the specified file list is cached in the page cache, and how much space is cached.
 
-Compared with pcstat, `pgcacher` has fixed the problem that the file list of the process is incorrect. It used to be obtained through `/proc/{pid}/maps`, but now it is changed to obtain from `/proc/{pid}/maps` and `/proc/{pid}/fd` at the same time. pgcacher supports more parameters, such as top, worker, depth, least-size, exclude-files and include-files. 😁
+Compared with pcstat, `pgcacher` has fixed the problem that the file list of the process is incorrect. It used to be obtained through `/proc/{pid}/maps`, but now it is changed to obtain from `/proc/{pid}/maps` and `/proc/{pid}/fd` at the same time. pgcacher supports more parameters, such as top, worker, limit, depth, least-size, exclude-files and include-files. 😁
 
 In addition, the pgcacher code is more robust, and also supports concurrency parameters, which can calculate the cache occupancy in the page cache faster. 
 
@@ -14,10 +14,11 @@ In addition, the pgcacher code is more robust, and also supports concurrency par
 
 ```sh
 pgcacher <-json <-pps>|-terse|-default> <-nohdr> <-bname> file file file
-    -depth set the depth of dirs to scan.
+    -limit limit the number of files displayed, default: 500
+    -depth set the depth of dirs to scan, default: 0
     -worker concurrency workers, default: 2
     -pid show all open maps for the given pid
-    -top scan the open files of all processes, show the top few files that occupy the most memory space in the page cache.
+    -top scan the open files of all processes, show the top few files that occupy the most memory space in the page cache, default: false
     -lease-size ignore files smaller than the lastSize, such as '10MB' and '15GB'
     -exclude-files exclude the specified files by wildcard, such as 'a*c?d' and '*xiaorui*,rfyiamcool'
     -include-files only include the specified files by wildcard, such as 'a*c?d' and '*xiaorui?cc,rfyiamcool'
@@ -114,7 +115,7 @@ chmod 777 pgcacher
 │ Sum        │ 10.746G        │ 2817091     │ 10.746G        │ 2817091     │ 100.000 │
 +------------+----------------+-------------+----------------+-------------+---------+
 
-# sudo pgcacher -top=3
+# sudo pgcacher -top -limit 3
 
 +------------------+----------------+-------------+----------------+-------------+---------+
 | Name             | Size           │ Pages       │ Cached Size    │ Cached Pages│ Percent │

main.go

@@ -12,8 +12,8 @@ import (
 )
 
 type option struct {
-	pid, top, worker, depth               int
-	terse, json, unicode                  bool
+	pid, worker, depth, limit             int
+	top, terse, json, unicode             bool
 	plain, bname                          bool
 	leastSize, excludeFiles, includeFiles string
 }
@@ -23,7 +23,8 @@ var globalOption = new(option)
 func init() {
 	// basic params
 	flag.IntVar(&globalOption.pid, "pid", 0, "show all open maps for the given pid")
-	flag.IntVar(&globalOption.top, "top", 0, "scan the open files of all processes, show the top few files that occupy the most memory space in the page cache.")
+	flag.IntVar(&globalOption.limit, "limit", 500, "limit the number of files displayed")
+	flag.BoolVar(&globalOption.top, "top", false, "scan the open files of all processes, show the top few files that occupy the most memory space in the page cache.")
 	flag.IntVar(&globalOption.depth, "depth", 0, "set the depth of dirs to scan")
 	flag.IntVar(&globalOption.worker, "worker", 2, "concurrency workers")
 	flag.StringVar(&globalOption.leastSize, "least-size", "0mb", "ignore files smaller than the lastSize, such as 10MB and 15GB")
@@ -51,10 +52,14 @@ func main() {
 	files = walkDirs(files, globalOption.depth)
 
 	// init pgcacher obj
-	pg := pgcacher{files: files, leastSize: int64(leastSize), option: globalOption}
+	pg := pgcacher{
+		files:     files,
+		leastSize: int64(leastSize),
+		option:    globalOption,
+	}
 
-	if globalOption.top != 0 {
-		pg.handleTop(globalOption.top)
+	if globalOption.top {
+		pg.handleTop()
 		os.Exit(0)
 	}
 
@@ -63,16 +68,20 @@ func main() {
 	}
 
 	if len(pg.files) == 0 {
-		fmt.Println("files is null ?")
+		fmt.Println("the files is null ???")
 		flag.Usage()
 		os.Exit(1)
 	}
 
 	pg.filterFiles()
 	stats := pg.getPageCacheStats()
-	pg.output(stats)
+	pg.output(stats, pg.option.limit)
 
 	// invalid function, just make a reference relationship with pcstat
+	invalidCall()
+}
+
+func invalidCall() {
 	pcstat.SwitchMountNs(os.Getegid())
 	pcstat.GetPcStatus(os.Args[0])
 }

pgcacher.go

@@ -231,7 +231,10 @@ func (pg *pgcacher) getPageCacheStats() PcStatusList {
 	return stats
 }
 
-func (pg *pgcacher) output(stats PcStatusList) {
+func (pg *pgcacher) output(stats PcStatusList, limit int) {
+	limit = min(len(stats), limit)
+	stats = stats[:limit]
+
 	if pg.option.json {
 		stats.FormatJson()
 	} else if pg.option.terse {
@@ -245,7 +248,7 @@ func (pg *pgcacher) output(stats PcStatusList) {
 	}
 }
 
-func (pg *pgcacher) handleTop(top int) {
+func (pg *pgcacher) handleTop() {
 	// get all active process.
 	procs, err := psutils.Processes()
 	if err != nil || len(procs) == 0 {
@@ -293,9 +296,11 @@ func (pg *pgcacher) handleTop(top int) {
 	// filter files
 	pg.filterFiles()
 
+	// get page cache stats of files.
 	stats := pg.getPageCacheStats()
-	top = min(len(stats), top)
-	pg.output(stats[:top])
+
+	// print
+	pg.output(stats, pg.option.limit)
 }
 
 func min(x, y int) int {