linux-kernel - Re: [-stable 3.8.1 performance regression] madvise POSIX_FADV

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Message-ID: <51D471DE.3020800@gmail.com>
Date:	Wed, 03 Jul 2013 14:47:58 -0400
From:	Yannick Brosseau <yannick.brosseau@...il.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Dave Chinner <david@...morbit.com>,
	Rob van der Heij <rvdheij@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	stable@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	"lttng-dev@...ts.lttng.org" <lttng-dev@...ts.lttng.org>
Subject: Re: [-stable 3.8.1 performance regression] madvise POSIX_FADV_DONTNEED

On 2013-07-03 04:47, Mel Gorman wrote:
>> Given it is just a hint, we should be allowed to perform page
>> > deactivation lazily. Is there any fundamental reason to wait for worker
>> > threads on each CPU to complete their lru drain before returning from
>> > fadvise() to user-space ?
>> > 
> Only to make sure they pages are actually dropped as requested. The reason
> the wait was introduced in the first place was that page cache was filling
> up even with the fadvise calls and causing disruption. In 3.11 disruption
> due to this sort of parallel IO should be reduced but making fadvise work
> properly is reasonable in itself. Was that patch I posted ever tested or
> did I manage to miss it?
I did test it. On our test case, we get a worst result with it.

Yannick
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