Re: [PATCH] kernel/fork: put some fork variables into read-mostly section

[Christian Brauner]

On Mon, Jan 13, 2020 at 11:23:13AM +0800, qiwuchen55@xxxxxxxxx wrote:
> From: chenqiwu <chenqiwu@xxxxxxxxxx>
> 
> Since total_forks/nr_threads/max_threads global variables are
> frequently used for process fork, putting these variables into
> read_mostly section can avoid unnecessary cache line bouncing.
> 
> Signed-off-by: chenqiwu <chenqiwu@xxxxxxxxxx>
> ---
>  kernel/fork.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0808095..163e152 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -120,10 +120,10 @@
>  /*
>   * Protected counters by write_lock_irq(&tasklist_lock)
>   */
> -unsigned long total_forks;	/* Handle normal Linux uptimes. */
> -int nr_threads;			/* The idle threads do not count.. */
> +unsigned long total_forks __read_mostly; /* Handle normal Linux uptimes. */
> +int nr_threads __read_mostly;  /* The idle threads do not count.. */

total_forks is incremented at every ~CLONE_THREAD and nr_threads at
CLONE_THREAD I wouldn't exactly say that this qualifies as mostly
reading.

>  
> -static int max_threads;		/* tunable limit on nr_threads */
> +static int max_threads __read_mostly; /* tunable limit on nr_threads */

That make sense.

Christian