On Tue, Sep 03, 2024 at 04:22:31PM -0700, Anthony Yznaga wrote: > This patch series implements a mechanism that allows userspace > processes to opt into sharing PTEs. It adds a new in-memory > filesystem - msharefs. A file created on msharefs represents a > shared region where all processes mapping that region will map > objects within it with shared PTEs. When the file is created, > a new host mm struct is created to hold the shared page tables > and vmas for objects later mapped into the shared region. This > host mm struct is associated with the file and not with a task. Taskless mm_struct can be problematic. Like, we don't have access to it's counters because it is not represented in /proc. For instance, there's no way to check its smaps. Also, I *think* it is immune to oom-killer because oom-killer looks for a victim task, not mm. I hope it is not an intended feature :P > When a process mmap's the shared region, a vm flag VM_SHARED_PT > is added to the vma. On page fault the vma is checked for the > presence of the VM_SHARED_PT flag. I think it is wrong approach. Instead of spaying VM_SHARED_PT checks across core-mm, we need to add a generic hooks that can be used by mshare and hugetlb. And remove is_vm_hugetlb_page() check from core-mm along the way. BTW, is_vm_hugetlb_page() callsites seem to be the indicator to check if mshare has to do something differently there. I feel you miss a lot of such cases. -- Kiryl Shutsemau / Kirill A. Shutemov
