Re: [PATCH] mm: Implement Swap Prefetching v25

From: David Lang
Date: Mon Feb 13 2006 - 16:18:12 EST

On Mon, 13 Feb 2006, Christoph Lameter wrote:

Date: Mon, 13 Feb 2006 13:16:00 -0800 (PST)
From: Christoph Lameter <clameter@xxxxxxxxxxxx>
To: David Lang <dlang@xxxxxxxxxxxxxxxxxx>
Cc: Con Kolivas <kernel@xxxxxxxxxxx>,
linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>,
Andrew Morton <akpm@xxxxxxxx>, ck list <ck@xxxxxxxxxxxxxxx>
Subject: Re: [PATCH] mm: Implement Swap Prefetching v25

On Mon, 13 Feb 2006, David Lang wrote:

On Mon, 13 Feb 2006, Christoph Lameter wrote:
spare ram when swapping??? We are already under memory pressure. Why make
it worse by getting rid of the few bits of available memory? If a system
swaps then we are per definition in the bad performance range. Add more
when a program exits it's memory is now free, rather then just waiting until
something uses this memory up normally, this patch attempts to fill that
memory with things that are expected to be useful (things that were swapped

Then trigger this action when a program exits and when you know there was
enough freed up to justify such an action. However, this is still a
heuristic. No one knows if the pages read from swap will be of any use at
all. For all I know a process may want to allocate some memory and fail
because the memory was needlessly spend to read in pages that no one

this won't happen, becouse if a program requests memory the kernel will through away data from the swap cache that's unchanged on disk (like the memory just filled by this) to free up memory for the program.

you don't want to trigger this on a program exit becouse the system is likly to be busy doing other things at that time, you want to try and do this when the system is otherwise idle.

David Lang

There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies.
-- C.A.R. Hoare

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