linux-kernel - Re: [PATCH 2/7] mm: shrinker: Add a .to

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Date:   Fri, 24 Nov 2023 11:08:11 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 2/7] mm: shrinker: Add a .to_text() method for shrinkers

Hi Kent,

On 2023/11/24 05:24, Kent Overstreet wrote:
> On Thu, Nov 23, 2023 at 11:32:59AM +0800, Qi Zheng wrote:
>>> +	void (*to_text)(struct seq_buf *, struct shrinker *);
>>
>> The "to_text" looks a little strange, how about naming it
>> "stat_objects"?
> 
> The convention I've been using heavily in bcachefs is
> typename_to_text(), or type.to_text(), for debug reports. The

OK.

> consistency is nice.

However, this is inconsistent with the name style of other
shrinker callbacks. Please use the "objects" suffix. As for
bcachefs's own callback function, you can use typename_to_text()
to ensure consistency.

Thanks,
Qi

> 
>>
>>>    	long batch;	/* reclaim batch size, 0 = default */
>>>    	int seeks;	/* seeks to recreate an obj */
>>> @@ -110,7 +114,6 @@ struct shrinker {
>>>    #endif
>>>    #ifdef CONFIG_SHRINKER_DEBUG
>>>    	int debugfs_id;
>>> -	const char *name;
>>
>> The name will only be allocated memory when the CONFIG_SHRINKER_DEBUG is
>> enabled, otherwise its value is NULL. So you can't move it out and use
>> it while CONFIG_SHRINKER_DEBUG is disabled.
> 
> Good catch
> 
>>> +void shrinkers_to_text(struct seq_buf *out)
>>> +{
>>> +	struct shrinker *shrinker;
>>> +	struct shrinker_by_mem {
>>> +		struct shrinker	*shrinker;
>>> +		unsigned long	mem;
>>
>> The "mem" also looks a little strange, how about naming it
>> "freeable"?
> 
> The type is just used in this one function, but sure.
> 
>>
>>> +	} shrinkers_by_mem[10];
>>> +	int i, nr = 0;
>>> +
>>> +	if (!mutex_trylock(&shrinker_mutex)) {
>>> +		seq_buf_puts(out, "(couldn't take shrinker lock)");
>>> +		return;
>>> +	}
>>
>> We now have lockless method (RCU + refcount) to iterate shrinker_list,
>> please refer to shrink_slab().
> 
> Will do!