Re: [RFC PATCH 0/6] Introduce Copy-On-Write to Page Table

Matthew Wilcox
2022-05-22T00:31:25Z

On Sat, May 21, 2022 at 03:19:24PM -0700, Andy Lutomirski wrote:
> I can see a rather different use for this type of shared-pagetable
> technology, though: monstrous MAP_SHARED mappings. For database and some VM
> users, multiple processes will map the same file. If there was a way to
> ensure appropriate alignment (or at least encourage it) and a way to handle
> mappings that don't cover the whole file, then having multiple mappings
> share the same page tables could be a decent efficiently gain. This doesn't
> even need COW -- it's "just" pagetable sharing.

The mshare proposal did not get a warm reception at LSFMM ;-(

The conceptual model doesn't seem to work for the MM developers who were
in the room. "Fear" was the most-used word. Not sure how we're going
to get to a model of sharing page tables that doesn't scare people.