Re: [PATCH] swapin readahead v3 + kswapd fixes

[Linus Torvalds <torvalds@transmeta.com>]

On Tue, 1 Dec 1998, Rik van Riel wrote:
> 
> --- ./mm/vmscan.c.orig	Thu Nov 26 11:26:50 1998
> +++ ./mm/vmscan.c	Tue Dec  1 07:12:28 1998
> @@ -431,6 +431,8 @@
>  	kmem_cache_reap(gfp_mask);
>  
>  	if (buffer_over_borrow() || pgcache_over_borrow())
> +		state = 0;		
> +	if (atomic_read(&nr_async_pages) > pager_daemon.swap_cluster / 2)
>  		shrink_mmap(i, gfp_mask);
>  
>  	switch (state) {

I really hate the above tests that make no sense at all from a conceptual
view, and are fairly obviously just something to correct for a more basic
problem. 

So I've removed them, and re-written the logic for the "state" in the VM
scanning. I made "state" be private to the invocation, and always start at
zero - and could thus remove it altogether. 

That means that the first thing freeing memory always tries to do is the
shrink_mmap() thing, and thus the problem becomes one of just making sure
that shrink_mmap() doesn't try _too_ aggressively to throw out stuff that
is still needed. So I changed shrink_mmap() too a bit, and simplified that
too (so that it looks at at most 1/32th of all memory on the first try,
and if it can't find anything to free there it lets the other memory
de-allocators have a go at it). 

It's a lot simpler, has no arbitrary heuristics like the above two tests,
and worked for me both with a small memory setup and my normal half gig
setup. Would you guys please test and comment? It's in the pre-2.1.132-1
patch. 

		Linus "arbitrary rules are bad rules" Torvalds

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