On Mon, Mar 28, 2011 at 05:44:21PM +0900, KAMEZAWA Hiroyuki wrote:
> On Mon, 28 Mar 2011 15:39:59 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
>
> > > In the global background reclaim, we do soft reclaim before scanning the
> > > per-zone LRU. However, the return value is ignored. This patch adds the logic
> > > where no per-zone reclaim happens if the soft reclaim raise the free pages
> > > above the zone's high_wmark.
> > >
> > > I did notice a similar check exists but instead leaving a "gap" above the
> > > high_wmark(the code right after my change in vmscan.c). There are discussions
> > > on whether or not removing the "gap" which intends to balance pressures across
> > > zones over time. Without fully understand the logic behind, I didn't try to
> > > merge them into one, but instead adding the condition only for memcg users
> > > who care a lot on memory isolation.
> > >
> > > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> >
> > Looks good to me. But this depend on "memcg soft limit" spec. To be honest,
> > I don't know this return value ignorance is intentional or not. So I think
> > you need to get ack from memcg folks.
> >
> >
> Hi,
>
>
> > > ---
> > > mm/vmscan.c | 16 +++++++++++++++-
> > > 1 files changed, 15 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 060e4c1..e4601c5 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -2320,6 +2320,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> > > int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
> > > unsigned long total_scanned;
> > > struct reclaim_state *reclaim_state = current->reclaim_state;
> > > + unsigned long nr_soft_reclaimed;
> > > struct scan_control sc = {
> > > .gfp_mask = GFP_KERNEL,
> > > .may_unmap = 1,
> > > @@ -2413,7 +2414,20 @@ loop_again:
> > > * Call soft limit reclaim before calling shrink_zone.
> > > * For now we ignore the return value
> > > */
> > > - mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
> > > + nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
> > > + order, sc.gfp_mask);
> > > +
> > > + /*
> > > + * Check the watermark after the soft limit reclaim. If
> > > + * the free pages is above the watermark, no need to
> > > + * proceed to the zone reclaim.
> > > + */
> > > + if (nr_soft_reclaimed && zone_watermark_ok_safe(zone,
> > > + order, high_wmark_pages(zone),
> > > + end_zone, 0)) {
> > > + __inc_zone_state(zone, NR_SKIP_RECLAIM_GLOBAL);
> >
> > NR_SKIP_RECLAIM_GLOBAL is defined by patch 2/2. please don't break bisectability.
> >
> >
> >
> > > + continue;
> > > + }
>
> Hmm, this "continue" seems not good to me. And, IIUC, this was a reason
> we ignore the result. But yes, ignore the result is bad.
> I think you should just do sc.nr_reclaimed += nr_soft_reclaimed.
> Or mem_cgroup_soft_limit_reclaim() should update sc.
>
>
> And allow kswapd to do some jobs as
> - call shrink_slab()
> - update total_scanned
> - update other flags.. etc...etc..
>
> If extra shink_zone() seems bad, please skip it, if mem_cgroup_soft_limit_reclaim()
> did enough jobs.
>
> IOW, mem_cgroup_soft_limit_reclaim() can't do enough jobs to satisfy
> ==
> 2426 balance_gap = min(low_wmark_pages(zone),
> 2427 (zone->present_pages +
> 2428 KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
> 2429 KSWAPD_ZONE_BALANCE_GAP_RATIO);
> 2430 if (!zone_watermark_ok_safe(zone, order,
> 2431 high_wmark_pages(zone) + balance_gap,
> 2432 end_zone, 0))
> 2433 shrink_zone(priority, zone, &sc);
> ==
Good point.
We should consider balancing the pressure on every zones.
> Thanks,
> -Kame
>
--
Kind regards,
Minchan Kim
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