Jim,
Thanks, the patch looks good to me. Yet I think you need to send V3 even
if I personally do not care ;) Please consider ./scripts/checkpatch.pl,
it reports all the coding-style problems I was going to mention.
I too have a couple of cosmetic nits, but feel free to ignore, this is
subjective.
On 03/09, Jim Newsome wrote:
>
> do_wait is an internal function used to implement waitpid, waitid,
> wait4, etc. To handle the general case, it does an O(n) linear scan of
> the thread group's children and tracees.
>
> This patch adds a special-case when waiting on a pid to skip these scans
> and instead do an O(1) lookup. This improves performance when waiting on
> a pid from a thread group with many children and/or tracees.
>
> Signed-off-by: James Newsome
> ---
> kernel/exit.c | 54 ++++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 45 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 04029e35e69a..312c4dfc9555 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1439,6 +1439,33 @@ void __wake_up_parent(struct task_struct *p, struct
> task_struct *parent)
> TASK_INTERRUPTIBLE, p);
> }
>
> +// Optimization for waiting on PIDTYPE_PID. No need to iterate through child
> +// and tracee lists to find the target task.
> +static int do_wait_pid(struct wait_opts *wo, struct task_struct *tsk)
> +{
> + struct task_struct *target = pid_task(wo->wo_pid, PIDTYPE_PID);
> + if (!target) {
> + return 0;
> + }
> + if (tsk == target->real_parent ||
> + (!(wo->wo_flags & __WNOTHREAD) &&
> + same_thread_group(tsk, target->real_parent))) {
> + int retval = wait_consider_task(wo, /* ptrace= */ 0, target);
> + if (retval) {
> + return retval;
> + }
> + }
> + if (target->ptrace && (tsk == target->parent ||
> + (!(wo->wo_flags & __WNOTHREAD) &&
> + same_thread_group(tsk, target->parent)))) {
> + int retval = wait_consider_task(wo, /* ptrace= */ 1, target);
> + if (retval) {
> + return retval;
> + }
> + }
Both if's use "int retval", to me it would be better to declare this variable
at the start of do_wait_pid(). But again, I won't insist this is up to you.
I am wondering if something like
static inline bool is_parent(struct task_struct *tsk, struct
task_struct *p, int flags)
{
return tsk == p || !(flags & __WNOTHREAD)) &&
same_thread_group(tsk, p);
}
makes any sense to make do_wait_pid() more clear... probably not.
Oleg.
