netdev - Re: [PATCH V3] fs: allow for more than 2^31 files

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Date:	Thu, 30 Sep 2010 15:26:12 -0500
From:	Robin Holt <holt@....com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, dipankar@...ibm.com,
	holt@....com, viro@...iv.linux.org.uk, bcrl@...ck.org,
	den@...nvz.org, mingo@...e.hu, mszeredi@...e.cz, cmm@...ibm.com,
	npiggin@...nel.dk, xemul@...nvz.org, linux-kernel@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH V3] fs: allow for more than 2^31 files

On Tue, Sep 28, 2010 at 05:46:51AM +0200, Eric Dumazet wrote:
> Le lundi 27 septembre 2010 à 15:36 -0700, David Miller a écrit :
...

> Fix is to let /proc/sys/fs/file-nr & /proc/sys/fs/file-max use long
> integers, and change af_unix to use an atomic_long_t instead of
> atomic_t.
> 
> get_max_files() is changed to return an unsigned long.

I _THINK_ we actually want get_max_files to return a long and have
the files_stat_struct definitions be longs.  If we do not have it that
way, we could theoretically open enough files on a single cpu to make
get_nr_files return a negative without overflowing max_files.  That,
of course, would require an insane amount of memory, but I think it is
technically more correct.

> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1352,16 +1352,16 @@ static struct ctl_table fs_table[] = {
>  	{
>  		.procname	= "file-nr",
>  		.data		= &files_stat,
> -		.maxlen		= 3*sizeof(int),
> +		.maxlen		= sizeof(files_stat),
>  		.mode		= 0444,
> -		.proc_handler	= proc_nr_files,
> +		.proc_handler	= proc_doulongvec_minmax,

With this change, don't we lose the current nr_files value?  I think
you need proc_nr_files to stay as it was.  If you disagree, we should
probably eliminate the definitions for proc_nr_files as I don't believe
they are used anywhere else.

Thanks,
Robin
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