Date: Sun, 25 Jan 2004 15:09:14 -0800
From: Andrew Morton <akpm@osdl.org>
To: Bart Samwel <bart@samwel.tk>
Cc: felix-kernel@fefe.de, linux-kernel@vger.kernel.org
Subject: Re: Request: I/O request recording
Message-Id: <20040125150914.1583d487.akpm@osdl.org>
In-Reply-To: <40144A36.5090709@samwel.tk>
References: <20040124181026.GA22100@codeblau.de>
	<20040124153551.24e74f63.akpm@osdl.org>
	<40144A36.5090709@samwel.tk>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1534
Lines: 30

Bart Samwel <bart@samwel.tk> wrote:
>
> When I saw this thread I've fiddled for a bit with the block_dump
>  functionality that's in the laptop_mode patch. I wanted to see if it
>  could support a similar thing completely from user space (except for the
>  block_dump code, of course). I've written a small tool to generate a
>  complete file that lists tuples (sector, size, device) from the kernel
>  output in syslog; it parses all "READ block xxx" messages since the
>  last reboot. Putting this through sort -n -u delivers a nicely sorted
>  file, ready for optimized reading.
> 
>  Unfortunately I'm now stuck within the other part, which is reading the
>  pages back in memory at the next boot. It's not working, and I was 
>  hoping someone here could take a look and tell me what I'm doing wrong.

Linux caches disk data on a per-file basis.  So if you preload pagecache
via the /dev/hda1 "file", that is of no benefit to the /etc/passwd file. 
Each one has its own unique pagecache.  When reading pages for /etc/passwd
we don't go looking for the same disk blocks in the cache of /dev/hda1.

Which is why the userspace cache preloading needs to know the pathnames of
all the relevant files - it needs to open and read each one, applying
knowledge of disk layout while doing it.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/