procfs: speed up /proc/pid/stat, statm

Process accounting applications as top, ps visit some files under
/proc/<pid>.  With seq_put_decimal_ull(), we can optimize /proc/<pid>/stat
and /proc/<pid>/statm files.

This patch adds
  - seq_put_decimal_ll() for signed values.
  - allow delimiter == 0.
  - convert seq_printf() to seq_put_decimal_ull/ll in /proc/stat, statm.

Test result on a system with 2000+ procs.

Before patch:
  [kamezawa@bluextal test]$ top -b -n 1 | wc -l
  2223
  [kamezawa@bluextal test]$ time top -b -n 1 > /dev/null

  real    0m0.675s
  user    0m0.044s
  sys     0m0.121s

  [kamezawa@bluextal test]$ time ps -elf > /dev/null

  real    0m0.236s
  user    0m0.056s
  sys     0m0.176s

After patch:
  kamezawa@bluextal ~]$ time top -b -n 1 > /dev/null

  real    0m0.657s
  user    0m0.052s
  sys     0m0.100s

  [kamezawa@bluextal ~]$ time ps -elf > /dev/null

  real    0m0.198s
  user    0m0.050s
  sys     0m0.145s

Considering top, ps tend to scan /proc periodically, this will reduce cpu
consumption by top/ps to some extent.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 7d19816c4cc9..55c293f7024d 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -659,7 +659,8 @@ int seq_put_decimal_ull(struct seq_file *m, char delimiter,
         if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
                 goto overflow;
 
-        m->buf[m->count++] = delimiter;
+        if (delimiter)
+                m->buf[m->count++] = delimiter;
 
         if (num < 10) {
                 m->buf[m->count++] = num + '0';
@@ -677,6 +678,24 @@ overflow:
 }
 EXPORT_SYMBOL(seq_put_decimal_ull);
 
+int seq_put_decimal_ll(struct seq_file *m, char delimiter,
+                        long long num)
+{
+        if (num < 0) {
+                if (m->count + 3 >= m->size) {
+                        m->count = m->size;
+                        return -1;
+                }
+                if (delimiter)
+                        m->buf[m->count++] = delimiter;
+                num = -num;
+                delimiter = '-';
+        }
+        return seq_put_decimal_ull(m, delimiter, num);
+
+}
+EXPORT_SYMBOL(seq_put_decimal_ll);
+
 /**
  * seq_write - write arbitrary data to buffer
  * @seq: seq_file identifying the buffer to which data should be written