On Thu, Oct 14, 2021 at 02:31:17PM +0200, Vlastimil Babka wrote:
> On 10/8/21 15:53, Mel Gorman wrote:
> > Memcg reclaim throttles on congestion if no reclaim progress is made.
> > This makes little sense, it might be due to writeback or a host of
> > other factors.
> >
> > For !memcg reclaim, it's messy. Direct reclaim primarily is throttled
> > in the page allocator if it is failing to make progress. Kswapd
> > throttles if too many pages are under writeback and marked for
> > immediate reclaim.
> >
> > This patch explicitly throttles if reclaim is failing to make progress.
> >
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> ...
> > @@ -3769,6 +3797,16 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> > trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
> > set_task_reclaim_state(current, NULL);
> >
> > + if (!nr_reclaimed) {
> > + struct zoneref *z;
> > + pg_data_t *pgdat;
> > +
> > + z = first_zones_zonelist(zonelist, sc.reclaim_idx, sc.nodemask);
> > + pgdat = zonelist_zone(z)->zone_pgdat;
> > +
> > + reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS, HZ/10);
> > + }
>
> Is this necessary? AFAICS here we just returned from:
>
> do_try_to_free_pages()
> shrink_zones()
> for_each_zone()...
> consider_reclaim_throttle()
>
> Which already throttles when needed and using the appropriate pgdat, while
> here we have to somewhat awkwardly assume the preferred one.
>
Yes, you're right, consider_reclaim_throttle not only throttles on the
appropriate pgdat but takes priority into account.
Well spotted!
--
Mel Gorman
SUSE Labs
