linux-kernel - Re: [PATCH 1/2] sched/wait: Break up long wake list walk

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

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?