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

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Message-ID: <4538ec3b.1052.196b839d0f1.Coremail.00107082@163.com>
Date: Sat, 10 May 2025 11:25:18 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Tim Chen" <tim.c.chen@...ux.intel.com>
Cc: surenb@...gle.com, kent.overstreet@...ux.dev, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between
 read() calls



At 2025-05-10 02:33:48, "Tim Chen" <tim.c.chen@...ux.intel.com> wrote:
>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

print_header flag will be set to false once header is printed, in allocinfo_show():
114         if (priv->print_header) {
115                 print_allocinfo_header(&buf);
116                 priv->print_header = false;
117         }

once priv->print_header) is set to true,  the header will be printed once and only once until it is 
set to true next time.

Thanks
David

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