[patch 095/166] proc: speed up /proc/*/statm

Andrew Morton
2020-04-07T03:09:07Z

From: Alexey Dobriyan <adobriyan@gmail.com>
Subject: proc: speed up /proc/*/statm

top(1) reads all /proc/*/statm files but kernel threads will always have
zeros. Print those zeroes directly without going through
seq_put_decimal_ull().

Speed up reading /proc/2/statm (which is kthreadd) is like 3%.

My system has more kernel threads than normal processes after booting KDE.

Link: http://lkml.kernel.org/r/20200307154435.GA2788@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/proc/array.c | 39 +++++++++++++++++++++++----------------
1 file changed, 23 insertions(+), 16 deletions(-)

--- a/fs/proc/array.c~proc-speed-up-proc-statm
+++ a/fs/proc/array.c
@@ -635,28 +635,35 @@ int proc_tgid_stat(struct seq_file *m, s
int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
- unsigned long size = 0, resident = 0, shared = 0, text = 0, data = 0;
struct mm_struct *mm = get_task_mm(task);

if (mm) {
+ unsigned long size;
+ unsigned long resident = 0;
+ unsigned long shared = 0;
+ unsigned long text = 0;
+ unsigned long data = 0;
+
size = task_statm(mm, &shared, &text, &data, &resident);
mmput(mm);
- }
- /*
- * For quick read, open code by putting numbers directly
- * expected format is
- * seq_printf(m, "%lu %lu %lu %lu 0 %lu 0\n",
- * size, resident, shared, text, data);
- */
- seq_put_decimal_ull(m, "", size);
- seq_put_decimal_ull(m, " ", resident);
- seq_put_decimal_ull(m, " ", shared);
- seq_put_decimal_ull(m, " ", text);
- seq_put_decimal_ull(m, " ", 0);
- seq_put_decimal_ull(m, " ", data);
- seq_put_decimal_ull(m, " ", 0);
- seq_putc(m, '\n');

+ /*
+ * For quick read, open code by putting numbers directly
+ * expected format is
+ * seq_printf(m, "%lu %lu %lu %lu 0 %lu 0\n",
+ * size, resident, shared, text, data);
+ */
+ seq_put_decimal_ull(m, "", size);
+ seq_put_decimal_ull(m, " ", resident);
+ seq_put_decimal_ull(m, " ", shared);
+ seq_put_decimal_ull(m, " ", text);
+ seq_put_decimal_ull(m, " ", 0);
+ seq_put_decimal_ull(m, " ", data);
+ seq_put_decimal_ull(m, " ", 0);
+ seq_putc(m, '\n');
+ } else {
+ seq_write(m, "0 0 0 0 0 0 0\n", 14);
+ }
return 0;
}

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