linux-kernel - Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV

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Date:	Wed, 15 Feb 2012 18:10:28 -0800
From:	Arun Sharma <asharma@...com>
To:	Andrea Righi <andrea@...terlinux.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Shaohua Li <shaohua.li@...el.com>,
	Pádraig Brady <P@...igBrady.com>,
	John Stultz <john.stultz@...aro.org>,
	Jerry James <jamesjer@...terlinux.com>,
	Julius Plenz <julius@...nz.com>, linux-mm <linux-mm@...ck.org>,
	<linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV_NOREUSE

On 2/15/12 4:56 PM, Andrea Righi wrote:

> Oh sorry, you're right! nocache_tree is not a pointer inside
> address_space, so the compiler must know the size.
>
> mmh... move the definition of the rb_root struct in linux/types.h? or
> simply use a rb_root pointer. The (void *) looks a bit scary and too bug
> prone.

Either way is fine. I did some black box testing of the patch (comparing 
noreuse vs dontneed) and it behaves as expected.

On a file copy, neither one pollutes the page cache. But if I run a 
random read benchmark on the source file right before and afterwards, 
page cache is warm with noreuse, but cold with dontneed. Copy 
performance was unaffected.

I can't really comment on the implementation details since I haven't 
reviewed it, but the functionality sounds useful.

  -Arun

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