Re: [PATCH V3 2/2] mm: page_alloc: enforce minimum zone size to do high atomic reserves

[David Rientjes]

On Fri, 24 Nov 2023, Charan Teja Kalla wrote:

> Highatomic reserves are set to roughly 1% of zone for maximum and a
> pageblock size for minimum.  Encountered a system with the below
> configuration:
> Normal free:7728kB boost:0kB min:804kB low:1004kB high:1204kB
> reserved_highatomic:8192KB managed:49224kB
> 
> On such systems, even a single pageblock makes highatomic reserves are
> set to ~8% of the zone memory. This high value can easily exert pressure
> on the zone.
> 
> Per discussion with Michal and Mel, it is not much useful to reserve
> the memory for highatomic allocations on such small systems[1]. Since
> the minimum size for high atomic reserves is always going to be a
> pageblock size and if 1% of zone managed pages is going to be below
> pageblock size, don't reserve memory for high atomic allocations. Thanks
> Michal for this suggestion[2].
> 
> Since no memory is being reserved for high atomic allocations and if
> respective allocation failures are seen, this patch can be reverted.
> 
> [1] https://lore.kernel.org/linux-mm/20231117161956.d3yjdxhhm4rhl7h2@xxxxxxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/linux-mm/ZVYRJMUitykepLRy@tiehlicka/
> 
> Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>