Re: [RFC PATCH] mm/khugepaged: cap pageblock contribution to min_free_kbytes

[Nimrod Oren]

On 17/07/2026 17:58, Zi Yan wrote:
> On 17 Jul 2026, at 9:36, Lorenzo Stoakes (ARM) wrote:
>> Maybe a simpler version would be to just attack the issue we actually have
>> with it - it uses too much damn memory :)
>>
>> So maybe something like the attached? (you'd probably want to make this a
>> sysctl or at least a defined value of course)
> 
> The approach below makes sense to me. In terms of the actual cap size,
> I asked Codex to check what possible pageblock_size and their reserved
> sizes:
> 
> 1. 1MB pageblock size (s390) and 11MB per zone,
> 2. 2MB pageblock size and 22MB per zone,
> 3. 8MB pageblock size and 88MB per zone,
> 4. 16MB pageblock size and 176MB per zone,
> 5. 32MB pageblock size and 352MB per zone,
> 6. 128MB pageblock size and 1.375GB per zone,
> 7. 512MB pageblock size and 5.5GB per zone.
> 
> 1GB makes sense to me. 512MB might also work.
> 

Assuming three eligible zones, my original proposal would have been
equivalent to a much lower cap of 66MB:

  2MB * 11 pageblocks per zone * 3 zones = 66MB

Using a more conservative value also sounds reasonable to me.

>> General idea is - if we're going to cap, let's just cap instead of
>> pretending that page blocks are of a different size.
>>
> 
> Sounds good to me. Thank you for the suggestion.
> 
Thanks Lorenzo and Zi for the review.
Capping the final recommendation directly sounds good to me.