Re: [PATCH 1/2] Add the soft_limit reclaim in global direct reclaim.

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, Apr 29, 2011 at 10:44:16AM -0700, Ying Han wrote:
> On Fri, Apr 29, 2011 at 6:05 AM, Michal Hocko <mhocko@suse.cz> wrote:
> > On Thu 28-04-11 15:37:05, Ying Han wrote:
> >> We recently added the change in global background reclaim which
> >> counts the return value of soft_limit reclaim. Now this patch adds
> >> the similar logic on global direct reclaim.

The changelog is a bit misleading: you don't just add something that
counts something.  You add code that can result in actual page
reclamation.

> >> @@ -1980,8 +1983,17 @@ static void shrink_zones(int priority, struct zonelist *zonelist,
> >>                               continue;       /* Let kswapd poll it */
> >>               }
> >>
> >> +             nr_soft_scanned = 0;
> >> +             nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
> >> +                                                     sc->order, sc->gfp_mask,
> >> +                                                     &nr_soft_scanned);
> >> +             sc->nr_reclaimed += nr_soft_reclaimed;
> >> +             total_scanned += nr_soft_scanned;
> >> +
> >>               shrink_zone(priority, zone, sc);
> >
> > This can cause more aggressive reclaiming, right? Shouldn't we check
> > whether shrink_zone is still needed?
> 
> We decided to leave the shrink_zone for now before making further
> changes for soft_limit reclaim. The same
> patch I did last time for global background reclaim. It is safer to do
> this step-by-step :)

I am sorry, but I kinda lost track of what's going on because there
are so many patches and concurrent discussions...  who is we and do
you have a pointer to the email where this conclusion was reached?

And safe how?  Do you want to trade a potential regression against a
certain one (overreclaim)?

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