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Date: Tue, 22 Aug 2017 20:56:24 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk
Message-ID: <20170822185624.GN32112@worktop.programming.kicks-ass.net>
References: <37D7C6CF3E00A74B8858931C1DB2F077537879BB@SHSMSX103.ccr.corp.intel.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Liang, Kan" <kan.liang@intel.com>, Mel Gorman <mgorman@techsingularity.net>, Mel Gorman <mgorman@suse.de>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Tim Chen <tim.c.chen@linux.intel.com>, Ingo Molnar <mingo@elte.hu>, Andi Kleen <ak@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>

On Tue, Aug 22, 2017 at 11:19:12AM -0700, Linus Torvalds wrote:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a49702445ce0..75c29a1f90fb 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -991,13 +991,11 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
>  			}
>  		}
>  
> -		if (lock) {
> -			if (!test_and_set_bit_lock(bit_nr, &page->flags))
> -				break;
> -		} else {
> -			if (!test_bit(bit_nr, &page->flags))
> -				break;
> -		}
> +		if (!lock)
> +			break;
> +
> +		if (!test_and_set_bit_lock(bit_nr, &page->flags))
> +			break;
>  	}

Won't we now prematurely terminate the wait when we get a spurious
wakeup?

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