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

[Liam R. Howlett]

* Kiryl Shutsemau <kas@xxxxxxxxxx> [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?

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.

Thanks,
Liam