On 09.09.20 15:14, Jason Gunthorpe wrote: > On Wed, Sep 09, 2020 at 01:32:44PM +0100, Matthew Wilcox wrote: > >> But here's the thing ... we already allow >> mmap(MAP_POPULATE | MAP_HUGETLB | MAP_HUGE_1GB) >> >> So if we're not doing THP, what's the point of this thread? > > I wondered that too.. > >> An madvise flag is a different beast; that's just letting the kernel >> know what the app thinks its behaviour will be. The kernel can pay > > But madvise is too late, the VMA already has an address, if it is not > 1G aligned it cannot be 1G THP already.
That's why user space (like QEMU) is THP-aware and selects an address that is aligned to the expected THP granularity (e.g., 2MB on x86_64). -- Thanks, David / dhildenb
