[TODO] `mmap()` file mapping & shared [file] mapping

[MarcoCicognani]

Suggestion

Hi Aaron,
Good to see you still working on the VM subsystem.

I put this issue as a memo for the missing features of the mmap() implementation.
I hope you are already at work on it.

Keep going man!

[byteduck]

Yep, that's exactly what I'm going to add next :) the hope is to use it in the linker to map program segments into memory to hopefully speed things up a little.

[MarcoCicognani]

It could be cool if the file mapping uses the VFS layer page-cache to share pages, in order to reduce memory usage

[byteduck]

That's what I'm hoping to do. Right now, the disk is cached at the block level, so it would rely on files being aligned at page boundaries. I may have to rework the VFS cache a little too.

[MarcoCicognani]

That's cool man!
Waiting for updates

[byteduck]

Update on this:

I've got inode mappings working on a basic level. Shared and private mappings both work, but more can definitely be done to speed things up. In no particular order, here's a list of things I still need to do:

• Allow for the partial copy-on-write of VMObjects. As in, copy each page as needed rather than copying the whole object when one page is written to.
• When mapping an inode privately with write permissions, use the shared mapping pages and mark them as CoW to speed things up.
• Add mremap and msync.
• Eliminate the block-level cache and just use the shared inode cache instead.
• Rewrite ld to use memory-mapped files to reduce memory usage as well as speed things up.

[MarcoCicognani]

Great Man!