linux-kernel - Re: [RESEND Patch] kcore: remove its pointless size

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Message-ID: <m14otwq94e.fsf@fess.ebiederm.org>
Date:	Wed, 01 Jul 2009 16:25:05 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Amerigo Wang <xiyou.wangcong@...il.com>, tao.ma@...cle.com,
	linux-kernel@...r.kernel.org, adobriyan@...il.com,
	mtk.manpages@...il.com
Subject: Re: [RESEND Patch] kcore: remove its pointless size

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Tue, 30 Jun 2009 18:08:50 +0800
> Amerigo Wang <xiyou.wangcong@...il.com> wrote:
>
>> 
>> Linus fixes wrong size of /proc/kcore problem in commit 9063c61fd5cbd.
>> 
>> But its size still looks insane, since it never equals to the size
>> of physical memory.
>
> Better changelogs, please!
>
> I think that what you're saying is that the stat.st_size field of the
> /proc/kcore inode does not equal the amount of physical memory, and
> that you think it should do so?
>
> If that is correct then it would be appropriate to explain what value
> the stat.st_size field has before the patch and afterwards.  Just
> calling it "insane" isn't optimal.
>
>> Signed-off-by: WANG Cong <amwang@...hat.com>
>> Cc: mtk.manpages@...il.com
>> 
>> (Andrew, could you please just cut off the kernel part from below? :)
>> 
>> ---
>> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
>> index 59b43a0..eca5201 100644
>> --- a/fs/proc/kcore.c
>> +++ b/fs/proc/kcore.c
>> @@ -405,9 +405,6 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
>>  static int __init proc_kcore_init(void)
>>  {
>>  	proc_root_kcore = proc_create("kcore", S_IRUSR, NULL, &proc_kcore_operations);
>> -	if (proc_root_kcore)
>> -		proc_root_kcore->size =
>> -				(size_t)high_memory - PAGE_OFFSET + PAGE_SIZE;
>>  	return 0;
>>  }
>>  module_init(proc_kcore_init);
>
> AFAICT this means that proc_root_kcore->size will remain uninitialised
> until a process opens and reads from /proc/kcore.  So on initial boot
> the `ls' output will presumably show a size of zero, and this will
> change once /proc/kcore has been read?

Which is better than showing a random number of dubious relationship
to the size we normally show.  That code is just a maintenance problem.

> If so, should we run get_kcore_size() in proc_kcore_init(), perhaps?
>
> In fact, do we need to run get_kcore_size() more than once per boot? 
>
> AFAICT we only run kclist_add() during bootup, so if proc_kcore_init()
> is called at the appropriate time, we can permanently cache its result?
>
> In which case get_kcore_size() and kclist_add() can be marked __init.
>
> Maybe that's all wrong - I didn't look terribly closely.

Memory hot add I expect is the excuse.  There is more that could be
done.  But this patch is an obvious bit of chipping away nonsense
code.

Eric

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