linux-kernel - Re: [PATCH v2 2/2] mm/damon/dbgfs: Add adaptive_targets list check before enable monitor

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Message-Id: <20211019154243.17474-1-sj@kernel.org>
Date:   Tue, 19 Oct 2021 15:42:43 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Xin Hao <xhao@...ux.alibaba.com>
Cc:     sjpark@...zon.de, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/damon/dbgfs: Add adaptive_targets list check before enable monitor_on

Hello Xin,

On Tue, 19 Oct 2021 22:26:04 +0800 Xin Hao <xhao@...ux.alibaba.com> wrote:

> When the ctx->adaptive_targets list is empty,
> i did some test on monitor_on interface like this.

s/i/I/

> 
> echo on > /sys/kernel/debug/damon/monitor_on
> [  851.988307] damon: kdamond (5390) starts

Could you please add four spaces in the beginning of this example terminal
outputs?  Also, I think confirming targets are empty like below before writing
'on' could make this example better.

    # cat /sys/kernel/debug/damon/target_ids
    #

or, like below.

    # echo > /sys/kernel/debug/damon/target_ids

> 
> 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 there adds a judgment in 'dbgfs_monitor_on_write',
> if the ctx->adaptive_targets list is empty, return -EINVAL.
> 
> Signed-off-by: Xin Hao <xhao@...ux.alibaba.com>
> ---
>  include/linux/damon.h |  1 +
>  mm/damon/core.c       |  5 +++++
>  mm/damon/dbgfs.c      | 10 ++++++++--
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 715dadd21f7c..06acf73fe9db 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -316,6 +316,7 @@ void damon_destroy_scheme(struct damos *s);
> 
>  struct damon_target *damon_new_target(unsigned long id);
>  void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
> +int damon_target_empty(struct damon_ctx *ctx);

Seems 'bool' would be better for the return type?

>  void damon_free_target(struct damon_target *t);
>  void damon_destroy_target(struct damon_target *t);
>  unsigned int damon_nr_regions(struct damon_target *t);
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 2f6785737902..c651b49249e5 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -156,6 +156,11 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
>  	list_add_tail(&t->list, &ctx->adaptive_targets);
>  }
> 
> +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);
> diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
> index 38188347d8ab..bac42dd358d1 100644
> --- a/mm/damon/dbgfs.c
> +++ b/mm/damon/dbgfs.c
> @@ -865,9 +865,15 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
>  		return -EINVAL;
>  	}
> 
> -	if (!strncmp(kbuf, "on", count))
> +	if (!strncmp(kbuf, "on", count)) {
> +		int i;
> +
> +		for (i = 0; i < dbgfs_nr_ctxs; i++) {
> +			if (damon_target_empty(dbgfs_ctxs[i]))
> +				return -EINVAL;
> +		}
>  		err = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs);
> -	else if (!strncmp(kbuf, "off", count))
> +	} else if (!strncmp(kbuf, "off", count))
>  		err = damon_stop(dbgfs_ctxs, dbgfs_nr_ctxs);
>  	else
>  		err = -EINVAL;

Please use braces for all above branches:

https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces


Thanks,
SJ

> --
> 2.31.0