Re: [PATCH] mm/damon/core: Optimize kdamod.%d thread creation code

[xhao@linux.alibaba.com]

On 2021/10/17 上午12:56, Xin Hao wrote:
> When the ctx->adaptive_targets list is empty,
> i did some test on monitor_on interface like this.
>
> echo on > /sys/kernel/debug/damon/monitor_on
> [  851.988307] damon: kdamond (5390) starts
>
> Though the ctx->adaptive_targets list is empty, but the
> kthread_run still be called, and the kdamond.x thread still
> be created, this is meaningless, so t

Sorry there made a mistake, i will send a new one.

>
> So there adds a judgment. only if the ctx->adaptive_targets
> list is not empty, and ctx->kdamond pointer is NULL, then call
> the __damon_start function.
>
> Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
> ---
>   mm/damon/core.c | 30 ++++++++++++++++++------------
>   1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 30e9211f494a..998c707fdca2 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -107,6 +107,11 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
>   	list_add_tail(&t->list, &ctx->adaptive_targets);
>   }
>   
> +static int damon_target_empty(struct damon_ctx *ctx)
> +{
> +	return list_empty(&ctx->adaptive_targets);
> +}
> +
>   static void damon_del_target(struct damon_target *t)
>   {
>   	list_del(&t->list);
> @@ -307,15 +312,14 @@ static int __damon_start(struct damon_ctx *ctx)
>   	int err = -EBUSY;
>   
>   	mutex_lock(&ctx->kdamond_lock);
> -	if (!ctx->kdamond) {
> +	ctx->kdamond_stop = false;
> +	ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
> +				   nr_running_ctxs);
> +	if (IS_ERR(ctx->kdamond)) {
> +		err = PTR_ERR(ctx->kdamond);
> +		ctx->kdamond = 0;
> +	} else {
>   		err = 0;
> -		ctx->kdamond_stop = false;
> -		ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
> -				nr_running_ctxs);
> -		if (IS_ERR(ctx->kdamond)) {
> -			err = PTR_ERR(ctx->kdamond);
> -			ctx->kdamond = 0;
> -		}
>   	}
>   	mutex_unlock(&ctx->kdamond_lock);
>   
> @@ -347,10 +351,12 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
>   	}
>   
>   	for (i = 0; i < nr_ctxs; i++) {
> -		err = __damon_start(ctxs[i]);
> -		if (err)
> -			break;
> -		nr_running_ctxs++;
> +		if (!damon_target_empty(ctxs[i]) && !ctxs[i]->kdamond) {
> +			err = __damon_start(ctxs[i]);
> +			if (err)
> +				break;
> +			nr_running_ctxs++;
> +		}
>   	}
>   	mutex_unlock(&damon_lock);
>   

-- 
Best Regards!
Xin Hao