On Tue, Jan 04, 2022 at 03:04:31PM -0800, Mina Almasry wrote: > On Mon, Dec 13, 2021 at 4:22 PM Mina Almasry <almasrymina@xxxxxxxxxx> wrote: > > > > On Sat, Nov 27, 2021 at 8:10 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > > > On Mon, Nov 22, 2021 at 04:01:02PM -0800, Mina Almasry wrote: > > > > Add PM_THP_MAPPED MAPPING to allow userspace to detect whether a given virt > > > > address is currently mapped by a transparent huge page or not. Example > > > > use case is a process requesting THPs from the kernel (via a huge tmpfs > > > > mount for example), for a performance critical region of memory. The > > > > userspace may want to query whether the kernel is actually backing this > > > > memory by hugepages or not. > > > > > > But what is userspace going to _do_ differently if the kernel hasn't > > > backed the memory with huge pages? > > > > Sorry for the late reply here. > > > > My plan is to expose this information as metrics right now and: > > 1. Understand the kind of hugepage backing we're actually getting if any. > > 2. If there are drops in hugepage backing we can investigate the > > cause, whether it's due to normal memory fragmentation or some > > bug/issue. > > 3. Schedule machines for reboots to defragment the memory if the > > hugepage backing is too low. > > 4. Possibly motivate future work to improve hugepage backing if our > > numbers are too low. > > Friendly ping on this. It has been reviewed by a few folks and after > Matthew had questions about the use case which I've answered in the > email above. Matthew, are you opposed to this patch? I'm not convinced you need more than the existing stats (THP_FAULT_FALLBACK) for the information you claim to want.
