linux-kernel - Re: [PATCH] mm: swap prefetch improvements

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Message-Id: <200705230850.01844.kernel@kolivas.org>
Date:	Wed, 23 May 2007 08:50:01 +1000
From:	Con Kolivas <kernel@...ivas.org>
To:	ck@....kolivas.org
Cc:	Ash Milsted <thatistosayiseenem@...ab.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: swap prefetch improvements

On Wednesday 23 May 2007 06:42, Ash Milsted wrote:
> Hi. I just did some video encoding on my desktop and I was noticing
> (for the first time in a while) that running apps had to hit swap quite
> a lot when I switched to them (the encoding was going at full blast for
> most of the day, and most of the time other running apps were
> idle). Now, a good half of my RAM appeared to be free during all this,
> so I was thinking at the time that it would be nice if swap prefetch
> could be tunably more aggressive. I guess it would be ideal in this
> case if it could kick in during tunably low disk-IO periods, even if
> the CPU is rather busy. I'm sure you've considered this, so I only butt
> in here to cast a vote for it. :)

In this case nicing the video encode should be enough to make it prefetch even 
during heavy cpu usage. It detects the total nice level rather than the cpu 
usage.

> Of course, I could be completely wrong about the possibility.. and I
> seem to remember that the disk cache can take up about half the ram by
> default without this showing up in 'gnome-system-monitor'... which I
> guess might happen during heavy encoding.. but even if it did, I could
> have set the limit lower, and would then have still appreciated
> prefetching.

I plan to make it prefetch more aggressively by default soon and make it more 
tunable too.

-- 
-ck
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