Re: [RFC PATCH 0/6] Add support for shared PTEs across processes

[Matthew Wilcox]

On Sat, Jan 22, 2022 at 11:18:14AM +0100, Thomas Schoebel-Theuer wrote:
> On 1/22/22 2:41 AM, Matthew Wilcox wrote:
> > On Sat, Jan 22, 2022 at 01:39:46AM +0000, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
> > > > > Our use case is that we have some very large files stored on persistent
> > > > > memory which we want to mmap in thousands of processes.  So the first
> > > The memory overhead of PTEs would be significantly saved if we use
> > > hugetlbfs in this case, but why not?
> > Because we want the files to be persistent across reboots.
> 
> 100% agree. There is another use case: geo-redundancy.
> 
> My view is publicly documented at
> https://github.com/schoebel/mars/tree/master/docu and click at
> architecture-guide-geo-redundancy.pdf

That's a 160+ page PDF.  No offence, Thomas, I'm not reading that to
try to understand how you want to use page table sharing.

> In some scenarios, migration or (temporary) co-existence of block devices
> from/between hardware architecture A to/between hardware architecture B
> might become a future requirement for me.

I'm not sure how sharing block devices between systems matches up with
sharing page tables between processes.

> It would be great if msharefs is not only low-footprint, but also would be
> usable from kernelspace.

I don't understand what you want here either.  Kernel threads already
share their page tables.