linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Message-ID: <52210225.60805@hp.com>
Date:	Fri, 30 Aug 2013 16:35:49 -0400
From:	Waiman Long <waiman.long@...com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On 08/30/2013 04:26 PM, Al Viro wrote:
> On Fri, Aug 30, 2013 at 03:52:49PM -0400, Waiman Long wrote:
>
>> So it is the mnput_no_expire() function that is doing all the
>> lg_global_lock() calls.
> Interesting...  So you are getting a lot of mntput() with ->mnt_ns being
> NULL?  I wonder which type it is...  Note that anything mounted will
> have non-NULL ->mnt_ns until umount and anything obtained via
> kern_mount/kern_mount_data will also have a non-NULL ->mnt_ns - until
> kern_unmount().
>
> Could you try to gather stats of that sort?  Normally that path should
> be only hit by fput() when we have a lazy-unmounted fs and close an opened
> file on it...
>
> I see one potential stupidity in that area (simple_pin_fs() ought to set
> ->mnt_ns, with simple_release_fs() clearing it), but there's not a lot
> of fs types that would use the damn thing...

The AIM7 test was run on a set of 16 ramdisk formated with ext3 
filesystem with the following mount options: 
barrier=0,async,noatime,nodiratime. Maybe that is a factor.

Regards,
Longman
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