linux-kernel - Re: fadvise DONTNEED implementation (or lack thereof)

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Date:	Wed, 17 Nov 2010 19:16:19 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ben Gamari <bgamari.foss@...il.com>,
	linux-kernel@...r.kernel.org, rsync@...ts.samba.org,
	linux-mm@...ck.org, Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: fadvise DONTNEED implementation (or lack thereof)

On Mon, Nov 15, 2010 at 11:48 PM, Rik van Riel <riel@...hat.com> wrote:
> On 11/15/2010 04:05 AM, Minchan Kim wrote:
>>
>> On Mon, Nov 15, 2010 at 5:47 PM, Peter Zijlstra<peterz@...radead.org>
>>  wrote:
>>>
>>> On Mon, 2010-11-15 at 15:07 +0900, Minchan Kim wrote:
>
>>>> I wonder what's the problem in Peter's patch 'drop behind'.
>>>> http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg179576.html
>>>>
>>>> Could anyone tell me why it can't accept upstream?
>>>
>>> Read the thread, its quite clear nobody got convinced it was a good idea
>>> and wanted to fix the use-once policy, then Rik rewrote all of
>>> page-reclaim.
>>>
>>
>> Thanks for the information.
>> I hope this is a chance to rethink about it.
>> Rik, Could you give us to any comment about this idea?


Sorry for late reply, Rik.

> At the time, there were all kinds of general problems
> in page reclaim that all needed to be fixed.  Peter's
> patch was mostly a band-aid for streaming IO.
>
> However, now that most of the other page reclaim problems
> seem to have been resolved, it would be worthwhile to test
> whether Peter's drop-behind approach gives an additional
> improvement.

Okay. I will have a time to make the workload for testing.

>
> I could see it help by getting rid of already-read pages
> earlier, leaving more space for read-ahead data.

Yes. Peter's logic breaks demotion if the page is in active list.
But I think if it's just active page like rsync's two touch, we have
to move tail of inactive although it's in active list.
I will look into this, too.

>
> I suspect it would do fairly little to protect the working
> set, because we do not scan the active file list at all
> unless it grows to be larger than the inactive file list.

Absolutely. But how about rsync's two touch?
It can evict working set.

I need the time for investigation.
Thanks for the comment.


>
> --
> All rights reversed
>



-- 
Kind regards,
Minchan Kim
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