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

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Message-ID: <20120216103944.GA1440@thinkpad>
Date:	Thu, 16 Feb 2012 11:39:44 +0100
From:	Andrea Righi <andrea@...terlinux.com>
To:	Arun Sharma <asharma@...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 Wed, Feb 15, 2012 at 06:10:28PM -0800, Arun Sharma wrote:
> 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

Arun, thank you very much for your review and testing. Probably we'll
move to a different, memcg-based solution, so I don't think I'll post
another version of this patch set as is. In case, I'll apply one of
the workarounds for the rb_root attribute.

Thanks,
-Andrea
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