On 10/14/21 15:03, Mel Gorman wrote:
> 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!
So with that part removed
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Thanks!
