Re: page pre-swapping + moving it on cache-list

[Jonathan Lundell <jlundell@pobox.com>]

At 2:21 PM +0100 2001-09-06, Alex Bligh - linux-kernel wrote:
>It's not keeping it two lists that prevents proper
>defragmentation. It's having it allocated all around
>memory, and never freeing the pages which prevent
>coalescence of areas, and thus either
>throwing away the data, or garbage collecting, that
>prevents defragmentation. We never free these pages
>either because they sit in an idle system (with
>no memory pressure) in places like
>inactive_dirty, or in caches, or, in an active
>system, because they are direct_reclaim'd out
>of inactive_clean etc., so never get freed [1].
>
>As this kind of garbage collection requires memcpy()
>etc., it might be harmless when the system is
>idle, but isn't going to be an attractive option when
>the system is busy thrashing away (though it might be
>possible to hueristically evict awkward pages
>preferentially, by aging them more harshly).

The problem with thrashing, is it not, is that we're not making 
forward progress because we're waiting for swap--that is to say, 
thrashing *is* an idle state of sorts, and so might be an ideal 
opportunity for gc methods that require heavy CPU involvement. It's 
not as if there's anything better to do....
-- 
/Jonathan Lundell.