AcoSail/kernel_optimize_test
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ext4: add sysfs attr /sys/fs/ext4/<disk>/journal_task

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This is useful for moving journal thread into cgroup or
for tracing it with ftrace/perf/blktrace.

For now the only way is `pgrep jbd2/$DISK` but this is not reliable:
name may be longer than "comm" limit and any task could mock it.

Attribute shows pid in current pid-namespace or 0 if task is unreachable.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Konstantin Khlebnikov 2019-02-21 11:49:27 -05:00 committed by Theodore Ts'o
parent 231fe82b56
commit bc1d69d615
2 changed files with 20 additions and 0 deletions
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7
Documentation/ABI/testing/sysfs-fs-ext4
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@ -109,3 +109,10 @@ Description:
write operation (since a 4k random write might turn
into a much larger write due to the zeroout
operation).
What: /sys/fs/ext4/<disk>/journal_task
Date: February 2019
Contact: "Theodore Ts'o" <tytso@mit.edu>
Description:
This file is read-only and shows the pid of journal thread in
current pid-namespace or 0 if task is unreachable.

13
fs/ext4/sysfs.c
View File

@ -30,6 +30,7 @@ typedef enum {
attr_feature,
attr_pointer_ui,
attr_pointer_atomic,
attr_journal_task,
} attr_id_t;
typedef enum {
@ -125,6 +126,14 @@ static ssize_t trigger_test_error(struct ext4_sb_info *sbi,
return count;
}
static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)
{
if (!sbi->s_journal)
return snprintf(buf, PAGE_SIZE, "<none>\n");
return snprintf(buf, PAGE_SIZE, "%d\n",
task_pid_vnr(sbi->s_journal->j_task));
}
#define EXT4_ATTR(_name,_mode,_id) \
static struct ext4_attr ext4_attr_##_name = { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
@ -188,6 +197,7 @@ EXT4_RW_ATTR_SBI_UI(msg_ratelimit_burst, s_msg_ratelimit_state.burst);
EXT4_RO_ATTR_ES_UI(errors_count, s_error_count);
EXT4_ATTR(first_error_time, 0444, first_error_time);
EXT4_ATTR(last_error_time, 0444, last_error_time);
EXT4_ATTR(journal_task, 0444, journal_task);
static unsigned int old_bump_val = 128;
EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val);
@ -217,6 +227,7 @@ static struct attribute *ext4_attrs[] = {
ATTR_LIST(errors_count),
ATTR_LIST(first_error_time),
ATTR_LIST(last_error_time),
ATTR_LIST(journal_task),
NULL,
};
@ -304,6 +315,8 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
return print_tstamp(buf, sbi->s_es, s_first_error_time);
case attr_last_error_time:
return print_tstamp(buf, sbi->s_es, s_last_error_time);
case attr_journal_task:
return journal_task_show(sbi, buf);
}
return 0;