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

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Date:	Thu, 30 Sep 2010 23:34:13 -0500
From:	Robin Holt <holt@....com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Robin Holt <holt@....com>, David Miller <davem@...emloft.net>,
	dipankar@...ibm.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 Thu, Sep 30, 2010 at 10:45:45PM +0200, Eric Dumazet wrote:
> Le jeudi 30 septembre 2010 à 15:26 -0500, Robin Holt a écrit :
> > 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.
> > 
> 
> Number of opened file is technically a positive (or null) value, I have
> no idea why you want it being signed.
> 
> > 
> > > --- 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.
> > 
> 
> I have no idea why you think I changed something. I only made the value
> use 64bit on 64bit arches, so that we are not anymore limited to 2^31
> files.

The proc_handler used to be proc_nr_files() which would call
get_nr_files() and deposit the result in files_stat.nr_files then cascade
to proc_dointvec() which would dump the 3 values.  Now it will dump the
three values, but not update the middle (nr_files) value first.

Robin
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