Re: [PATCH] vmscan: fix missing place to check nr_swap_pages.

[Ying Han <yinghan@google.com>]

On Thu, Aug 26, 2010 at 10:00 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
>
> On Fri, Aug 27, 2010 at 12:31 PM, Ying Han <yinghan@google.com> wrote:
> > On Thu, Aug 26, 2010 at 6:03 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
> >>
> >> Hello.
> >>
> >> On Fri, Aug 27, 2010 at 9:11 AM, Ying Han <yinghan@google.com> wrote:
> >> > Fix a missed place where checks nr_swap_pages to do shrink_active_list. Make the
> >> > change that moves the check to common function inactive_anon_is_low.
> >> >
> >>
> >> Hmm.. AFAIR, we discussed it at that time but we concluded it's not good.
> >> That's because nr_swap_pages < 0 means both "NO SWAP" and "NOT enough
> >> swap space now". If we have a swap device or file but not enough space
> >> now, we need to aging anon pages to make inactive list enough size.
> >> Otherwise, working set pages would be swapped out more fast before
> >> promotion.
> >
> > We found the problem on one of our workloads where more TLB flush
> > happens without the change. Kswapd seems to be calling
> > shrink_active_list() which eventually clears access bit of those ptes
> > and does TLB flush
> > with ptep_clear_flush_young(). This system does not have swap
> > configured, and why aging the anon lru in that
> > case?
>
> True. I also wanted it but we have to care swap configured but
> non-enabling still yet system as well as non-swap configured system at
> that time.

Agree.  In our case, we cares about the case where swap is not enabled
but is configured .
>
> If your system is no swap configured, how about this?
> (It's a not formal proper patch but just quick patch to show the concept)