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

[Rik van Riel <H.H.vanRiel@phys.uu.nl>]

On 22 Dec 1998, Eric W. Biederman wrote:

> The goal is to keep one single rogue program from outcompeting all
> of the others. With implementing a RSS limit this is accomplished
> by at some point forcing free pages to come from the program that
> needs the memory, (via swap_out) instead of directly.
> 
> What currently happens is when such a program starts thrashing, is
> whenever it wakes up it steals all of the memory, and sleeps until
> it can steel some more.  Because the program is a better
> competitor, than the others.  With a RSS limit we would garantee
> that there is some memory left over for other programs to run in.
> 
> Eventually we should attempt to autotune a programs RSS by it's
> workload, and if giving a program a larger RSS doesn't help (that
> is the program continues to thrash with an RSS we give it) we
> should scale back it's RSS, so as not to compete with other
> programs.

I have a better idea:

if (current->mm->rss > hog_pct && total_mapped > syshog_pct) {
    ... swap_out_process(current, GFP)  swap_cluster pages ...
}

We can easily do something like this because swap_out() only
unmaps the pages and they can easily be mapped in again.

I know we tried it before and it horribly failed back then,
but now pages are not freed on swap_out(). Things have changed
in such a way that it could probably work now...

We want the above routine in one of the functions surrounding
mm/page_alloc.c::swap_in() -- this way we 'throttle at the
source'.

I know some of you think throttling at the source is a bad
thing (even for buffer cache), but you'll have to throttle
eventually and not doing it will mean you also 'throttle'
the (innocent) rest of the system...

cheers,

Rik -- the flu hits, the flu hits, the flu hits -- MORE
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| Linux memory management tour guide.        H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader.      http://www.phys.uu.nl/~riel/ |
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