Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86

[Kiryl Shutsemau <kas@kernel.org>]

On Thu, Feb 19, 2026 at 10:28:20PM -0500, Liam R. Howlett wrote:
> * Kiryl Shutsemau <kas@kernel.org> [260219 17:05]:
> > On Thu, Feb 19, 2026 at 09:08:57AM -0800, Dave Hansen wrote:
> > > On 2/19/26 07:08, Kiryl Shutsemau wrote:
> > > >   - The order-0 page size cuts struct page overhead by a factor of 16. From
> > > >     ~1.6% of RAM to ~0.1%;
> > > ...
> > > But, it will mostly be getting better performance at the _cost_ of
> > > consuming more RAM, not saving RAM.
> > 
> > That's fair.
> > 
> > The problem with struct page memory consumption is that it is static and
> > cannot be reclaimed. You pay the struct page tax no matter what.
> > 
> > Page cache rounding overhead can be large, but a motivated userspace can
> > keep it under control by avoiding splitting a dataset into many small
> > files. And this memory is reclaimable.
> > 
> 
> But we are in reclaim a lot more these days.  As I'm sure you are aware,
> we are trying to maximize the resources (both cpu and ram) of any
> machine powered on.  Entering reclaim will consume the cpu time and will
> affect other tasks.
> 
> Especially with multiple workload machines, the tendency is to have a
> primary focus with the lower desired work being killed, if necessary.
> Reducing the overhead just means more secondary tasks, or a bigger
> footprint of the ones already executing.
> 
> Increasing the memory pressure will degrade the primary workload more
> frequently, even if we recover enough to avoid OOMing the secondary.
> 
> While in the struct page tax world, the secondary task would be killed
> after a shorter (and less frequently executed) reclaim comes up short.
> So, I would think that we would be degrading the primary workload in an
> attempt to keep the secondary alive?  Maybe I'm over-simplifying here?

I am not sure I fully follow your point.

Sizing tasks and scheduling tasks between machines is hard in general.
I don't think the balance between struct page tax and page cache
rounding overhead is going to be the primary factor.

> Near the other end of the spectrum, we have chromebooks that are
> constantly in reclaim, even with 4k pages.  I guess these machines would
> be destine to maintain the same page size they use today.  That is, this
> solution for the struct page tax is only useful if you have a lot of
> memory.  But then again, that's where the bookkeeping costs become hard
> to take.

Smaller machines are not target for 64k pages. They will not benefit
from them.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov