linux-kernel - Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched files

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Message-ID: <20150622132821.GB12596@twins.programming.kicks-ass.net>
Date:	Mon, 22 Jun 2015 15:28:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Dave Hansen <dave@...1.net>, Andi Kleen <ak@...ux.intel.com>,
	dave.hansen@...ux.intel.com, akpm@...ux-foundation.org,
	jack@...e.cz, viro@...iv.linux.org.uk, eparis@...hat.com,
	john@...nmccutchan.com, rlove@...ve.org,
	tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched
 files

On Sat, Jun 20, 2015 at 06:30:58PM -0700, Paul E. McKenney wrote:
> Well, it is not hard to have an SRCU-like thing that doesn't have
> read-side memory barriers, given that older versions of SRCU didn't
> have them.  However, the price is increased latency for the analog to
> synchronize_srcu().  I am guessing that this would not be a problem
> for notification-group destruction, which is presumably rare.

I don't think it ever makes sense to optimize for a global state. So
screw sync_srcu() and make the srcu_read_lock() thing go fast.

If you need fast global state you're doing it wrong.
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