Date: Tue, 25 Feb 2014 11:49:24 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Michael wang <wangyun@linux.vnet.ibm.com>
Cc: Sasha Levin <sasha.levin@oracle.com>, Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: sched: hang in migrate_swap
Message-ID: <20140225104924.GK9987@twins.programming.kicks-ass.net>
References: <5305856F.3000109@linux.vnet.ibm.com>
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 <530ABB44.5000601@oracle.com>
 <530AD653.3000808@linux.vnet.ibm.com>
 <20140224071028.GW9987@twins.programming.kicks-ass.net>
 <530B1B80.4000307@linux.vnet.ibm.com>
 <20140224121218.GR15586@twins.programming.kicks-ass.net>
 <20140224131025.GG3104@twins.programming.kicks-ass.net>
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On Tue, Feb 25, 2014 at 12:47:01PM +0800, Michael wang wrote:
> On 02/24/2014 09:10 PM, Peter Zijlstra wrote:
> > On Mon, Feb 24, 2014 at 01:12:18PM +0100, Peter Zijlstra wrote:
> >> +		if (p) {
> >> +			if (unlikely(p == RETRY_TASK))
> >> +				goto again;
> > 
> > We could even make that: unlikely(p & 1), I think most CPUs can encode
> > that far better than the full pointer immediate.
> 
> Agree, unless odd-align stuff appeared...

That shouldn't happen; we rely on u32 alignment all over the place. So
for general objects we should have at least the lower two bits free to
play with.
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