Re: New patch (was Re: [PATCH] swapin readahead v3 + kswapd fixes)

[Andrea Arcangeli <andrea@e-mind.com>]

On Sat, 19 Dec 1998, Stephen C. Tweedie wrote:

>I've tried to port the best bits of that VM to 132-pre2, preserving your
>do_try_to_free_page state change, but so far I have not been able find a
>combination which gives anywhere near the overall performance of ac11
>for all of my test cases (although it works reasonably well on low
			   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>memory at first, until we start to fragment swap).

The good point of 132-pre2 is that you' ll never see a thread on linux
kernel that will say "132-pre2 VM performance jerky". It could be not
the best but sure will work well for everybody out there on every
hardware. 132-pre2 policy is "if you need great performance buy more
memory" swap will work fine but it' s not the default action. I agree to
help improving it though. 

>The patch below is the best I have so far against 132-pre2.  You will
>find that it has absolutely no references to the borrow percentages, and
>although it does honour the buffer/pgcache min percentages, those
>default to 1%.

I agree also to drop every borrow/max check in the kernel since we don' t
want a limit on the cache/buffer used until there is free memory. If a
special software need a lot of memory at once can grab it slowly and then
mlock it I think.

Index: linux/fs/buffer.c
diff -u linux/fs/buffer.c:1.1.1.1 linux/fs/buffer.c:1.1.1.1.2.1
--- linux/fs/buffer.c:1.1.1.1	Fri Nov 20 00:01:06 1998
+++ linux/fs/buffer.c	Thu Dec 17 22:35:20 1998
@@ -725,8 +725,7 @@
 	/* We are going to try to locate this much memory. */
 	needed = bdf_prm.b_un.nrefill * size;  
 
-	while ((nr_free_pages > freepages.min*2) &&
-	        !buffer_over_max() &&
+	while (free_memory_available() == 2 &&
 		grow_buffers(GFP_BUFFER, size)) {
 		obtained += PAGE_SIZE;
 		if (obtained >= needed)


Alternatively we could set the default of max to 90% or something
similar... probably it would be more tunable but I like more the
total autotuning approch...

Andrea Arcangeli

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