From: Peter Zijlstra <peterz@infradead.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
Rik van Riel <riel@redhat.com>, linux-mm <linux-mm@kvack.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: page_waitqueue() considered harmful
Date: Tue, 27 Sep 2016 18:52:21 +0200 [thread overview]
Message-ID: <20160927165221.GP5016@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160928005318.2f474a70@roar.ozlabs.ibm.com>
On Wed, Sep 28, 2016 at 12:53:18AM +1000, Nicholas Piggin wrote:
> The more interesting is the ability to avoid the barrier between fastpath
> clearing a bit and testing for waiters.
>
> unlock(): lock() (slowpath):
> clear_bit(PG_locked) set_bit(PG_waiter)
> test_bit(PG_waiter) test_bit(PG_locked)
>
> If this was memory ops to different words, it would require smp_mb each
> side.. Being the same word, can we avoid them?
Ah, that is the reason I put that smp_mb__after_atomic() there. You have
a cute point on them being to the same word though. Need to think about
that.
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next prev parent reply other threads:[~2016-09-27 16:52 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 20:58 page_waitqueue() considered harmful Linus Torvalds
2016-09-26 21:23 ` Rik van Riel
2016-09-26 21:30 ` Linus Torvalds
2016-09-26 23:11 ` Kirill A. Shutemov
2016-09-27 1:01 ` Rik van Riel
2016-09-27 7:30 ` Peter Zijlstra
2016-09-27 8:54 ` Mel Gorman
2016-09-27 9:11 ` Kirill A. Shutemov
2016-09-27 9:42 ` Mel Gorman
2016-09-27 9:52 ` Minchan Kim
2016-09-27 12:11 ` Kirill A. Shutemov
2016-09-29 8:01 ` Peter Zijlstra
2016-09-29 12:55 ` Nicholas Piggin
2016-09-29 13:16 ` Peter Zijlstra
2016-09-29 13:54 ` Nicholas Piggin
2016-09-29 15:05 ` Rik van Riel
2016-09-27 8:03 ` Jan Kara
2016-09-27 8:31 ` Mel Gorman
2016-09-27 14:34 ` Peter Zijlstra
2016-09-27 15:08 ` Nicholas Piggin
2016-09-27 16:31 ` Linus Torvalds
2016-09-27 16:49 ` Peter Zijlstra
2016-09-28 10:45 ` Mel Gorman
2016-09-28 11:11 ` Peter Zijlstra
2016-09-28 16:10 ` Linus Torvalds
2016-09-29 13:08 ` Peter Zijlstra
2016-10-03 10:47 ` Mel Gorman
2016-09-27 14:53 ` Nicholas Piggin
2016-09-27 15:17 ` Nicholas Piggin
2016-09-27 16:52 ` Peter Zijlstra [this message]
2016-09-27 17:06 ` Nicholas Piggin
2016-09-28 7:05 ` Peter Zijlstra
2016-09-28 11:05 ` Paul E. McKenney
2016-09-28 11:16 ` Peter Zijlstra
2016-09-28 12:58 ` Paul E. McKenney
2016-09-29 1:31 ` Nicholas Piggin
2016-09-29 2:12 ` Paul E. McKenney
2016-09-29 6:21 ` Peter Zijlstra
2016-09-29 6:42 ` Nicholas Piggin
2016-09-29 7:14 ` Peter Zijlstra
2016-09-29 7:43 ` Peter Zijlstra
2016-09-28 7:40 ` Mel Gorman
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