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Date: Wed, 15 Feb 2012 18:10:28 -0800
From: Arun Sharma <asharma@fb.com>
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Subject: Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV_NOREUSE
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To: Andrea Righi <andrea@betterlinux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan.kim@gmail.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Johannes Weiner <jweiner@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Shaohua Li <shaohua.li@intel.com>, =?UTF-8?B?UMOhZHJhaWcgQnJhZHk=?= <P@draigBrady.com>, John Stultz <john.stultz@linaro.org>, Jerry James <jamesjer@betterlinux.com>, Julius Plenz <julius@plenz.com>, linux-mm <linux-mm@kvack.org>, linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>

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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