On Mon, Sep 21, 2020 at 9:19 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > On Tue, 15 Sep 2020, Dan Williams wrote: > > > > TODO: > > > > > > - programs run approximately 4% slower when running from Optane-based > > > persistent memory. Therefore, programs and libraries should use page cache > > > and not DAX mapping. > > > > This needs to be based on platform firmware data f(ACPI HMAT) for the > > relative performance of a PMEM range vs DRAM. For example, this > > tradeoff should not exist with battery backed DRAM, or virtio-pmem. > > Hi > > I have implemented this functionality - if we mmap a file with > (vma->vm_flags & VM_DENYWRITE), then it is assumed that this is executable > file mapping - the flag S_DAX on the inode is cleared on and the inode > will use normal page cache. > > Is there some way how to test if we are using Optane-based module (where > this optimization should be applied) or battery backed DRAM (where it > should not)? No, there's no direct reliable type information. Instead the firmware on ACPI platforms provides the HMAT table which provides performance details of system-memory ranges.
