Re: try_to_swap_out() return value problem?

[Rik van Riel]

On Thu, 4 Jan 2001, Linus Torvalds wrote:
> On Thu, 4 Jan 2001, Rik van Riel wrote:
> > On Wed, 3 Jan 2001, Linus Torvalds wrote:
> > > On Thu, 4 Jan 2001, Marcelo Tosatti wrote:
> > 
> > > I agree that the return value of swap_out() is fairly meaningless. It's
> > > been fairly meaningless for a long time now, and it's entirely possible
> > > that the "while (swap_out())" loop should be just something like
> > > 
> > > 	/* Scan the VM space, try to clean up the page tables a bit */
> > > 	for (i = 0 ; i <= nr_threads >> priority; i++)
> > > 		swap_out(gfp_mask);
> > 
> > The problem with this is that it means that page aging of
> > the mapped active pages is no longer balanced against the
> > aging of the unmapped active pages.
> 
> Is there any reason to not just remove the lines
> 
>         if (!onlist)
>                 /* The page is still mapped, so it can't be freeable... */
>                 age_page_down_ageonly(page);
> 
>         /*
>          * If the page is in active use by us, or if the page
>          * is in active use by others, don't unmap it or
>          * (worse) start unneeded IO.
>          */
>         if (page->age > 0)
>                 goto out_failed;
> 
> from vmscan?
> 
> They look like a complete hack, although an understandable one
> from the time when the virtual memory scan used to actually do
> IO as well.
>
> These days, if you think of the VM scanning as just a "shrink
> the page tables" operation, the down-aging doesn't make much
> sense. That will happen once the page has been moved to the
> lists, no?

Hmmmm, I'm not sure ...

I can't quite put my finger on it, but my gut feeling
says that removing this lines could unbalance the page
aging and/or cause other nasties.

Then again, in theory the current VM should already be
unbalanced and we haven't felt any bad effects yet ;)

regards,

Rik
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