linux-kernel - Re: [PATCH 2/4] fs/dcache: Report negative dentry number in dentry-state

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Date:   Mon, 17 Jul 2017 10:39:11 -0400
From:   Waiman Long <longman@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>
Subject: Re: [PATCH 2/4] fs/dcache: Report negative dentry number in
 dentry-state

On 07/17/2017 10:09 AM, Matthew Wilcox wrote:
> On Mon, Jul 17, 2017 at 09:39:31AM -0400, Waiman Long wrote:
>> @@ -63,9 +63,10 @@ struct qstr {
>>  struct dentry_stat_t {
>>  	long nr_dentry;
>>  	long nr_unused;
>> -	long age_limit;          /* age in seconds */
>> -	long want_pages;         /* pages requested by system */
>> -	long dummy[2];
>> +	long nr_negative;	/* # of negative dentries */
>> +	long age_limit;		/* age in seconds */
>> +	long want_pages;	/* pages requested by system */
>> +	long dummy;
>>  };
>>  extern struct dentry_stat_t dentry_stat;
> You can't just insert a field in the middle like that.  It'll break any code
> parsing /proc/sys/fs/dentry-state.  You have to put it at the end:
>
>  	long age_limit;          /* age in seconds */
>  	long want_pages;         /* pages requested by system */
> -	long dummy[2];
> +	long nr_negative;	/* # of negative dentries */
> +	long dummy;
>  };

My mistake. I will send out an updated patches later on after collecting
more feedback to make the new field go to the end.

Cheers,
Longman