Re: [PATCH] mm, vmscan: make kswapd unreserve highatomic pageblocks

[Vlastimil Babka (SUSE)]

On 11/4/26 22:56, Jose A. Perez de Azpillaga wrote:
> On 11/4/26 7:38 PM, Vlastimil Babka (SUSE) wrote:
>> Hook this highatomic unreserve to the moment we are increasing kswapd
>> reclaim priority, as that is when kswapd is struggling to make progress
>> and it should roughly match the case of direct reclaim failure.
>> 
> 
> isn't raise_priority true after almost every pass at DEF_PRIORITY, stuck
> or not?

Can you elaborate why? At least at first glance, kswapd_shrink_node() should
return true if it scans the requested amount of pages. So I would assume
that although balance_pgdat() will do multiple iterations to reach high
watermarks (because every round of kswapd_shrink_node() will limit itself to
SWAP_CLUSTER_MAX per zone for sc->nr_to_reclaim) this should not be raising
priority if the rounds are successful?

> [snip]
> 
>> +		if (raise_priority || !nr_reclaimed) {
>> +			/*
>> +			 * Similarly to when direct reclaim is retrying, try to
>> +			 * unreserve highatomic pageblocks on the node. Convert
>> +			 * them to movable ones as kswapd doesn't have a target
>> +			 * migratetype, and passing unmovable should lead to
>> +			 * least permanent fragmentation.
>> +			 */
>> +			for (int i = 0; i <= highest_zoneidx; i++) {
>> +				struct zone *zone = pgdat->node_zones + i;
>> +
>> +				unreserve_highatomic_pageblock_zone(zone,
>> +						MIGRATE_UNMOVABLE, false);
>> +			}
> s/movable/unmovable/ in the comment?
>