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

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

On 11/5/26 9:02 AM, Vlastimil Babka (SUSE) wrote:
> 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?
> 


it's max(high_wmark_pages(zone), SWAP_CLUSTER_MAX) per zone, so the sum
of the high watermarks. by default that's at least managed/500, while
DEF_PRIORITY scans lru >> 12, so it can't return true above priority 8
even when every round is successful. and sc.priority-- runs before
pgdat_balanced() is rechecked, so a wakeup that balances the node in one
pass still unreserves a pageblock per zone.

-- 
cheers,
jose a. p-a