Message-ID: <4F3C6594.3030709@fb.com>
Date: Wed, 15 Feb 2012 18:10:28 -0800
From: Arun Sharma <asharma@fb.com>
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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>
Subject: Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV_NOREUSE
References: <1329006098-5454-1-git-send-email-andrea@betterlinux.com> <1329006098-5454-4-git-send-email-andrea@betterlinux.com> <20120215233537.GA20724@dev3310.snc6.facebook.com> <20120215234724.GA21685@thinkpad> <4F3C467B.1@fb.com> <20120216005608.GC21685@thinkpad>
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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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