Re: [DATAPOINT] pre7-6 will not swap

[Rajagopal Ananthanarayanan <ananth@sgi.com>]

"Quintela Carreira Juan J." wrote:
> 
> >>>>> "linus" == Linus Torvalds <torvalds@transmeta.com> writes:
> 
> linus> in vmscan.c, and that seems to be quite well-behaved too (but if somebody
> linus> has the energy to test the two different versions, I'd absolutely love to
> linus> hear results..)
> 
> Hi Linus,
>    I have tested two versions of the patch (against vanilla
> pre7-6), the first was to remove the test altogether (I think this is
> from Rajagopal):
> 
> --- pre7-6/mm/vmscan.c  Fri May  5 23:58:56 2000
> +++ testing/mm/vmscan.c Mon May  8 23:30:52 2000
> @@ -114,8 +114,9 @@
>          * Don't do any of the expensive stuff if
>          * we're not really interested in this zone.
>          */
> -       if (!page->zone->zone_wake_kswapd)
> +/*     if (!page->zone->zone_wake_kswapd)
>                 goto out_unlock;
> +*/
> 

I'm having the same experience too. The one thing
that makes stuff better is not to look at the zone at all
in try_to_swap_out (as Juan points out above).

I'm trying to also see if we can do better in shrink_mmap().
Although my gprof statistics say that we can end-up spending
91% of the time skipping pages, I'm not able to comeup with
anything simple to make shrink_mmap behave better ... except
one change which makes swapping a lot less and shrink_mmap
a lot more agressive: don't skip pages based on zone's
high water mark if we are trying hard to free pages (my heuristic
was to stop skipping pages if priority in shrink_mmap was 3; YMMV).
I'm not entirely convinced that this is the right thing to do.

In all, I do think that try_to_swap_out shouldn't skip pages
based on zones. We have now evidence from 3 different "workloads"
in this direction --- my own dbench test, Juan's test above &
Benjamin's "gaming" workload.


--------------------------------------------------------------------------
Rajagopal Ananthanarayanan ("ananth")
Member Technical Staff, SGI.
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