add-dirtytime-sysctl-tuning-knob

   1 fs: add dirtytime_expire_seconds sysctl
   2
   3 Add a tuning knob so we can adjust the dirtytime expiration timeout,
   4 which is very useful for testing lazytime.
   5
   6 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
   7 ---
   8  fs/fs-writeback.c         | 5 ++++-
   9  include/linux/writeback.h | 1 +
  10  kernel/sysctl.c           | 8 ++++++++
  11  3 files changed, 13 insertions(+), 1 deletion(-)
  12
  13 diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
  14 index e907052..705f036 100644
  15 --- a/fs/fs-writeback.c
  16 +++ b/fs/fs-writeback.c
  17 @@ -53,6 +53,9 @@ struct wb_writeback_work {
  18         struct completion *done;        /* set if the caller waits */
  19  };
  20
  21 +/* 24 hours in seconds */
  22 +unsigned int dirtytime_expire_interval = 24 * 60 * 60;
  23 +
  24  /**
  25   * writeback_in_progress - determine whether there is writeback in progress
  26   * @bdi: the device's backing_dev_info structure.
  27 @@ -276,7 +279,7 @@ static int move_expired_inodes(struct list_head *delaying_queue,
  28         if ((flags & EXPIRE_DIRTY_ATIME) == 0)
  29                 older_than_this = work->older_than_this;
  30         else if ((work->reason == WB_REASON_SYNC) == 0) {
  31 -               expire_time = jiffies - (HZ * 86400);
  32 +               expire_time = jiffies - (dirtytime_expire_interval * HZ);
  33                 older_than_this = &expire_time;
  34         }
  35         while (!list_empty(delaying_queue)) {
  36 diff --git a/include/linux/writeback.h b/include/linux/writeback.h
  37 index 0004833..ba65fd0 100644
  38 --- a/include/linux/writeback.h
  39 +++ b/include/linux/writeback.h
  40 @@ -130,6 +130,7 @@ extern int vm_dirty_ratio;
  41  extern unsigned long vm_dirty_bytes;
  42  extern unsigned int dirty_writeback_interval;
  43  extern unsigned int dirty_expire_interval;
  44 +extern unsigned int dirtytime_expire_interval;
  45  extern int vm_highmem_is_dirtyable;
  46  extern int block_dump;
  47  extern int laptop_mode;
  48 diff --git a/kernel/sysctl.c b/kernel/sysctl.c
  49 index 88ea2d6..44e6a25 100644
  50 --- a/kernel/sysctl.c
  51 +++ b/kernel/sysctl.c
  52 @@ -1228,6 +1228,14 @@ static struct ctl_table vm_table[] = {
  53                 .extra1         = &zero,
  54         },
  55         {
  56 +               .procname       = "dirtytime_expire_seconds",
  57 +               .data           = &dirtytime_expire_interval,
  58 +               .maxlen         = sizeof(dirty_expire_interval),
  59 +               .mode           = 0644,
  60 +               .proc_handler   = proc_dointvec_minmax,
  61 +               .extra1         = &zero,
  62 +       },
  63 +       {
  64                 .procname       = "nr_pdflush_threads",
  65                 .mode           = 0444 /* read-only */,
  66                 .proc_handler   = pdflush_proc_obsolete,