linux-kernel - Re: [PATCH 10/15] readahead: add /debug/readahead/stats

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Date:	Thu, 25 Feb 2010 17:40:17 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Chris Mason <chris.mason@...cle.com>,
	Clemens Ladisch <clemens@...isch.de>,
	Olivier Galibert <galibert@...ox.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>,
	Matt Mackall <mpm@...enic.com>, Nick Piggin <npiggin@...e.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/15] readahead: add /debug/readahead/stats

On 02/23/2010 10:10 PM, Wu Fengguang wrote:
> Collect readahead stats when CONFIG_READAHEAD_STATS=y.
>
> This is enabled by default because the added overheads are trivial:
> two readahead_stats() calls per readahead.
>
> Example output:
> (taken from a fresh booted NFS-ROOT box with rsize=16k)
>
> $ cat /debug/readahead/stats
> pattern     readahead    eof_hit  cache_hit         io    sync_io    mmap_io       size async_size    io_size
> initial           524        216         26        498        498         18          7          4          4
> subsequent        181         80          1        130         13         60         25         25         24
> context            94         28          3         85         64          8          7          2          5
> thrash              0          0          0          0          0          0          0          0          0
> around            162        121         33        162        162        162         60          0         21
> fadvise             0          0          0          0          0          0          0          0          0
> random            137          0          0        137        137          0          1          0          1
> all              1098        445         63       1012        874          0         17          6          9
>
> The two most important columns are
> - io		number of readahead IO
> - io_size	average readahead IO size
>
> CC: Ingo Molnar<mingo@...e.hu>
> CC: Jens Axboe<jens.axboe@...cle.com>
> CC: Peter Zijlstra<a.p.zijlstra@...llo.nl>
> Signed-off-by: Wu Fengguang<fengguang.wu@...el.com>

Acked-by: Rik van Riel <riel@...hat.com>
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