linux-kernel - Re: [RFC v9 4/8] mm/damon/schemes: Implement a debugfs interface

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Date:   Thu, 4 Jun 2020 13:17:57 +0200
From:   SeongJae Park <sjpark@...zon.com>
To:     SeongJae Park <sjpark@...zon.com>
CC:     <akpm@...ux-foundation.org>, SeongJae Park <sjpark@...zon.de>,
        <Jonathan.Cameron@...wei.com>, <aarcange@...hat.com>,
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Subject: Re: [RFC v9 4/8] mm/damon/schemes: Implement a debugfs interface

On Tue, 26 May 2020 09:56:58 +0200 SeongJae Park <sjpark@...zon.com> wrote:

> From: SeongJae Park <sjpark@...zon.de>
> 
> This commit implements a debugfs interface for the data access
> monitoring oriented memory management schemes.  It is supposed to be
> used by administrators and/or privileged user space programs.  Users can
> read and update the rules using ``<debugfs>/damon/schemes`` file.  The
> format is::
> 
>     <min/max size> <min/max access frequency> <min/max age> <action>
> 
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
> ---
>  mm/damon.c | 176 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 174 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/damon.c b/mm/damon.c
> index 6a07649d1f5d..bcc732e8735c 100644
> --- a/mm/damon.c
> +++ b/mm/damon.c
> @@ -173,6 +173,29 @@ static void damon_destroy_task(struct damon_task *t)
>  	damon_free_task(t);
>  }
> +
> +/*
> + * Converts a string into an array of struct damos pointers
> + *
> + * Returns an array of struct damos pointers that converted if the conversion
> + * success, or NULL otherwise.
> + */
> +static struct damos **str_to_schemes(const char *str, ssize_t len,
> +				ssize_t *nr_schemes)
> +{
> +	struct damos *scheme, **schemes;
> +	const int max_nr_schemes = 256;
> +	int pos = 0, parsed, ret;
> +	unsigned int min_sz, max_sz, min_nr_a, max_nr_a, min_age, max_age;
> +	unsigned int action;
> +
> +	schemes = kmalloc_array(max_nr_schemes, sizeof(scheme),
> +			GFP_KERNEL);
> +	if (!schemes)
> +		return NULL;
> +
> +	*nr_schemes = 0;
> +	while (pos < len && *nr_schemes < max_nr_schemes) {
> +		ret = sscanf(&str[pos], "%u %u %u %u %u %u %u%n",
> +				&min_sz, &max_sz, &min_nr_a, &max_nr_a,
> +				&min_age, &max_age, &action, &parsed);
> +		if (ret != 7)
> +			break;
> +		if (action >= DAMOS_ACTION_LEN) {
> +			pr_err("wrong action %d\n", action);
> +			goto fail;
> +		}
> +
> +		pos += parsed;
> +		scheme = damon_new_scheme(min_sz, max_sz, min_nr_a, max_nr_a,
> +				min_age, max_age, action);
> +		if (!scheme)
> +			goto fail;
> +
> +		schemes[*nr_schemes] = scheme;
> +		*nr_schemes += 1;
> +	}
> +	if (!*nr_schemes)
> +		goto fail;
> +	return schemes;
> +fail:
> +	free_schemes_arr(schemes, *nr_schemes);
> +	return NULL;
> +}
> +
> +static ssize_t debugfs_schemes_write(struct file *file, const char __user *buf,
> +		size_t count, loff_t *ppos)
> +{
> +	struct damon_ctx *ctx = &damon_user_ctx;
> +	char *kbuf;
> +	struct damos **schemes;
> +	ssize_t nr_schemes = 0, ret;
> +	int err;
> +
> +	if (*ppos)
> +		return -EINVAL;
> +
> +	kbuf = kmalloc(count, GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;
> +
> +	ret = simple_write_to_buffer(kbuf, count, ppos, buf, count);
> +	if (ret < 0)
> +		goto out;
> +
> +	schemes = str_to_schemes(kbuf, ret, &nr_schemes);

In case of wrong input, 'str_to_schemes()' could return NULL with non-zero
nr_schemes, but the case is not handled here.  I will properly handle the case
in the next spin.


Thanks,
SeongJae Park

> +
> +	mutex_lock(&ctx->kdamond_lock);
> +	if (ctx->kdamond) {
> +		ret = -EBUSY;
> +		goto unlock_out;
> +	}
> +
> +	err = damon_set_schemes(ctx, schemes, nr_schemes);
> +	if (err)
> +		ret = err;
> +	else
> +		nr_schemes = 0;
> +unlock_out:
> +	mutex_unlock(&ctx->kdamond_lock);
> +	free_schemes_arr(schemes, nr_schemes);
> +out:
> +	kfree(kbuf);
> +	return ret;
> +}
> +