linux-kernel - Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between read() calls

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Message-ID: <7f237574d9f08a9fa8dcaa60d2edf8d8e91441d4.camel@linux.intel.com>
Date: Fri, 09 May 2025 11:33:48 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: David Wang <00107082@....com>, surenb@...gle.com,
 kent.overstreet@...ux.dev,  akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between
 read() calls

On Sat, 2025-05-10 at 01:39 +0800, David Wang wrote:
> 
> 
> Signed-off-by: David Wang <00107082@....com>
> ---
>  lib/alloc_tag.c | 29 ++++++++++-------------------
>  1 file changed, 10 insertions(+), 19 deletions(-)
> 
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index 25ecc1334b67..fdd5887769a6 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -45,21 +45,16 @@ struct allocinfo_private {
>  static void *allocinfo_start(struct seq_file *m, loff_t *pos)
>  {
>  	struct allocinfo_private *priv;
> -	struct codetag *ct;
>  	loff_t node = *pos;
>  
> -	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> -	m->private = priv;
> -	if (!priv)
> -		return NULL;
> -
> -	priv->print_header = (node == 0);
> +	priv = (struct allocinfo_private *)m->private;
>  	codetag_lock_module_list(alloc_tag_cttype, true);
> -	priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> -	while ((ct = codetag_next_ct(&priv->iter)) != NULL && node)
> -		node--;
> -
> -	return ct ? priv : NULL;
> +	if (node == 0) {
> +		priv->print_header = true;
> +		priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> +		codetag_next_ct(&priv->iter);
> +	}

Do you need to skip print header when *pos != 0? i.e add

	} else {
		priv->print_header = false;
	}

Tim

> +	return priv->iter.ct ? priv : NULL;
>  }
>