On 4/11/22 09:05, Khalid Aziz wrote: > PTEs are shared at pgdir level and hence it imposes following > requirements on the address and size given to the mshare(): > > - Starting address must be aligned to pgdir size (512GB on x86_64). > This alignment value can be looked up in /proc/sys/vm//mshare_size > - Size must be a multiple of pgdir size > - Any mappings created in this address range at any time become > shared automatically > - Shared address range can have unmapped addresses in it. Any access > to unmapped address will result in SIGBUS > > Mappings within this address range behave as if they were shared > between threads, so a write to a MAP_PRIVATE mapping will create a > page which is shared between all the sharers. The first process that > declares an address range mshare'd can continue to map objects in > the shared area. All other processes that want mshare'd access to > this memory area can do so by calling mshare(). After this call, the > address range given by mshare becomes a shared range in its address > space. Anonymous mappings will be shared and not COWed. What does this mean in practice?
