On Sat, May 21, 2022, at 5:31 PM, Matthew Wilcox wrote: > 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. FWIW, I didn’t like mshare. mshare was weird: it seemed to have one mm own some page tables and other mms share them. I’m talking about having a *file* own page tables and mms map them. This seems less fear-inducing to me. Circular dependencies are impossible, mmap calls don’t need to propagate, etc. It would still be quite a change, though.
