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Date: Tue, 20 Feb 2018 09:39:37 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        hjl.tools@gmail.com
Subject: Re: [PATCH 4/4] fs/dcache: Avoid the try_lock loops in dentry_kill()
Message-ID: <20180220083937.GX25201@hirez.programming.kicks-ass.net>
References: <20180216150933.971-1-john.ogness@linutronix.de>
 <20180216150933.971-5-john.ogness@linutronix.de>
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 <87r2pk358g.fsf@linutronix.de>
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On Tue, Feb 20, 2018 at 12:34:57AM +0100, John Ogness wrote:
> Implementation 2: Using switch on a dentry_lock_inode() that returns a
> tristate value. Does not support branch prediction. This approach is
> probably easiest to understand.
> 
>  		/*
>  		 * Lock the inode. Might drop dentry->d_lock temporarily
>  		 * which allows inode to change. Start over if that happens.
>  		 */
>                 switch (dentry_lock_inode(dentry)) {
>                 case LOCK_FAST:

Bah, I just checked, you cannot use GCC label attributes on statements
:/ Otherwise you could've done:

		case LOCK_FAST: __attribute__((hot));

>                         break;
>                 case LOCK_SLOW:
>                         /*
>                          * Recheck refcount as it might have been
>                          * incremented while d_lock was dropped.
>                          */
>                         if (unlikely(dentry->d_lockref.count != 1))
>                                 goto drop_ref;
>                         break;
>                 case LOCK_FAILED:
>                         goto again;
>                 }
>