From: Andrei Vagin <avagin@xxxxxxxxxx>
Subject: procfs: optimize seq_pad() to speed up /proc/pid/maps
seq_printf() is slow and it can be replaced by memset() in this case.
== test.py
num = 0
with open("/proc/1/maps") as f:
while num < 10000 :
data = f.read()
f.seek(0, 0)
num = num + 1
==
== Before patch ==
$ time python test.py
real 0m0.986s
user 0m0.279s
sys 0m0.707s
== After patch ==
$ time python test.py
real 0m0.932s
user 0m0.261s
sys 0m0.669s
$ perf record -g python test.py
== Before patch ==
- 47.35% 3.38% python [kernel.kallsyms] [k] show_map_vma.isra.23
- 43.97% show_map_vma.isra.23
+ 20.84% seq_path
- 15.73% show_vma_header_prefix
+ 6.96% seq_pad
+ 2.94% __GI___libc_read
== After patch ==
- 44.01% 0.34% python [kernel.kallsyms] [k] show_pid_map
- 43.67% show_pid_map
- 42.91% show_map_vma.isra.23
+ 21.55% seq_path
- 15.68% show_vma_header_prefix
+ 2.08% seq_pad
0.55% seq_putc
Link: http://lkml.kernel.org/r/20180112185812.7710-2-avagin@xxxxxxxxxx
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/seq_file.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff -puN fs/seq_file.c~procfs-optimize-seq_pad-to-speed-up-proc-pid-maps fs/seq_file.c
--- a/fs/seq_file.c~procfs-optimize-seq_pad-to-speed-up-proc-pid-maps
+++ a/fs/seq_file.c
@@ -828,8 +828,14 @@ EXPORT_SYMBOL(seq_write);
void seq_pad(struct seq_file *m, char c)
{
int size = m->pad_until - m->count;
- if (size > 0)
- seq_printf(m, "%*s", size, "");
+ if (size > 0) {
+ if (size + m->count > m->size) {
+ seq_set_overflow(m);
+ return;
+ }
+ memset(m->buf + m->count, ' ', size);
+ m->count += size;
+ }
if (c)
seq_putc(m, c);
}
_
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