Re: [LSF/MM/BPF BoF Session] Numa-Aware Placement for Page Cache Pages

[Matthew Wilcox <willy@infradead.org>]

On Thu, Apr 30, 2026 at 05:03:37PM +0530, Ritesh Harjani (IBM) wrote:
> Linux already supports memory tiers and there are ongoing discussions around
> promotion of unmapped page cache pages, which lets kernel do the right thing
> for userspace page cache pages on a tiered system.

Well, you know my opinion of that idea ...

> So the question is:
> Do we need a userspace interface for the placement policy of page cache pages on a per file basis?

What do we do if two tasks both "know" the right NUMA placement for the
inode's data, and they disagree?

> 1. Is there a need for an interface that allows userspace to do per-fd page
>    placement and maybe per-fd page migration?

Ideally, no, the kernel should observe the task and get it right.

By the way, you're familiar with how filemap_alloc_folio_noprof()
works today, right?  I forget whether cpuset_do_page_mem_spread
is on or off by default.

> Let me know if people think that this discussion qualifies for a BoF discussion at LSFMM?
> Or do you think it's a bad idea altogether, if that is the case - Then
> please help me understand, why so?
> Before starting to jump on the implemention of any of this - I would
> like to gather feedback on what do others think?

I'm just concerned about what other session i'll have to miss to attend
this instead ;-)