linux-kernel - Re: [patch v3] swap: virtual swap readahead

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Date:	Thu, 11 Jun 2009 12:17:42 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	"Barnes, Jesse" <jesse.barnes@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andi Kleen <andi@...stfloor.org>,
	Minchan Kim <minchan.kim@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch v3] swap: virtual swap readahead

On Thu, Jun 11, 2009 at 01:22:28PM +0800, Wu Fengguang wrote:
> Unfortunately, after fixing it up the swap readahead patch still performs slow
> (even worse this time):

Thanks for doing the tests.  Do you know if the time difference comes
from IO or CPU time?

Because one reason I could think of is that the original code walks
the readaround window in two directions, starting from the target each
time but immediately stops when it encounters a hole where the new
code just skips holes but doesn't abort readaround and thus might
indeed read more slots.

I have an old patch flying around that changed the physical ra code to
use a bitmap that is able to represent holes.  If the increased time
is waiting for IO, I would be interested if that patch has the same
negative impact.

	Hannes

>   before       after
>     0.02        0.01    N xeyes
>     0.76        0.89    N firefox
>     1.88        2.21    N nautilus
>     3.17        3.41    N nautilus --browser
>     4.89        5.20    N gthumb
>     6.47        7.02    N gedit
>     8.16        8.90    N xpdf /usr/share/doc/shared-mime-info/shared-mime-info-spec.pdf
>    12.55       13.36    N xterm
>    14.57       15.57    N mlterm
>    17.06       18.11    N gnome-terminal
>    18.90       20.37    N urxvt
>    23.48       25.26    N gnome-system-monitor
>    26.52       27.84    N gnome-help
>    29.65       31.93    N gnome-dictionary
>    36.12       37.74    N /usr/games/sol
>    39.27       40.61    N /usr/games/gnometris
>    42.56       43.75    N /usr/games/gnect
>    47.03       47.85    N /usr/games/gtali
>    52.05       52.31    N /usr/games/iagno
>    55.42       55.61    N /usr/games/gnotravex
>    61.47       61.38    N /usr/games/mahjongg
>    67.11       65.07    N /usr/games/gnome-sudoku
>    75.15       70.36    N /usr/games/glines
>    79.70       74.96    N /usr/games/glchess
>    88.48       80.82    N /usr/games/gnomine
>    96.51       88.30    N /usr/games/gnotski
>   102.19       94.26    N /usr/games/gnibbles
>   114.93      102.02    N /usr/games/gnobots2
>   125.02      115.23    N /usr/games/blackjack
>   135.11      128.41    N /usr/games/same-gnome
>   154.50      153.05    N /usr/bin/gnome-window-properties
>   162.09      169.53    N /usr/bin/gnome-default-applications-properties
>   173.29      190.32    N /usr/bin/gnome-at-properties
>   188.21      212.70    N /usr/bin/gnome-typing-monitor
>   199.93      236.18    N /usr/bin/gnome-at-visual
>   206.95      261.88    N /usr/bin/gnome-sound-properties
>   224.49      304.66    N /usr/bin/gnome-at-mobility
>   234.11      336.73    N /usr/bin/gnome-keybinding-properties
>   248.59      374.03    N /usr/bin/gnome-about-me
>   276.27      433.86    N /usr/bin/gnome-display-properties
>   304.39      488.43    N /usr/bin/gnome-network-preferences
>   342.01      686.68    N /usr/bin/gnome-mouse-properties
>   388.58      769.21    N /usr/bin/gnome-appearance-properties
>   508.47      933.35    N /usr/bin/gnome-control-center
>   587.57     1193.27    N /usr/bin/gnome-keyboard-properties
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