brody-qq 8812410617 Kernel/Memory: Fix redundant page faults on anonymous mmaps after fork ...

After a fork(), page faults on anonymous mmaps can cause a redundant
page fault to occur.

This happens because VMObjects for anonymous mmaps are initially filled
with references to the lazy_committed_page or shared_zero_page. If there
is a fork, VMObject::try_clone() is called and all pages of the VMObject
are marked as cow (via the m_cow_map).

Page faults on a zero/lazy page are handled by handle_zero_fault().
handle_zero_fault() does not update m_cow_map, so if the page was marked
cow before the fault, it will still be marked cow after the fault. This
causes a second (redundant) page fault when the CPU retries the write.

This commit removes the redundant page fault by not marking zero/lazy
pages as cow in m_cow_map.

2024-07-12 08:52:06 -04:00

3.7 KiB

Raw Blame History

View Raw