Subject: Re: [PATCH 0/7] breaking the global file_list_lock
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Christoph Hellwig <hch@infradead.org>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20070128151122.GA21159@infradead.org>
References: <20070128115118.837777000@programming.kicks-ass.net>
	 <20070128144325.GB16552@infradead.org>
	 <20070128151122.GA21159@infradead.org>
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Date: Sun, 28 Jan 2007 16:29:04 +0100
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On Sun, 2007-01-28 at 15:11 +0000, Christoph Hellwig wrote:

> > Even if this is becoming a real problem there must be simpler ways to fix
> > this than introducing various new locking primitives and all kinds of
> > complexity.
> 
> One good way to fix scalability without all this braindamage is
> to get rid of sb->s_files.  Current uses are:
> 
>  - fs/dquot.c:add_dquot_ref()
> 
> 	This performs it's actual operation on inodes.  We should
> 	be able to check inode->i_writecount to see which inodes
> 	need quota initialization.
> 
>  - fs/file_table.c:fs_may_remount_ro()
> 
> 	This one is gone in Dave Hansens per-mountpoint r/o patchkit
> 
>  - fs/proc/generic.c:proc_kill_inodes()
> 
> 	This can be done with a list inside procfs.
> 
>  - fs/super.c:mark_files_ro()
> 
> 	This one is only used for do_emergency_remount(), which is
> 	and utter hack.  It might be much better to just deny any
> 	kind of write access through a superblock flag here.
> 
>  - fs/selinuxfs.c:sel_remove_bools()
> 
> 	Utter madness.  I have no idea how this ever got merged.
> 	Maybe the selinux folks can explain what crack they were
> 	on when writing this.  The problem would go away with
> 	a generic rewoke infrastructure.
> 
> Once sb->s_files is gone we can also kill of fu_list entirely and
> replace it by a list head entirely in the tty code and make the lock
> for it per-tty.

I shall pursue this direction. Thanks for the information.

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