On Fri, Aug 05, 2022 at 03:22:58PM +0200, David Hildenbrand wrote: > On 06.07.22 10:20, Chao Peng wrote: > > This patch introduces memfile_notifier facility so existing memory file > > subsystems (e.g. tmpfs/hugetlbfs) can provide memory pages to allow a > > third kernel component to make use of memory bookmarked in the memory > > file and gets notified when the pages in the memory file become > > invalidated. > > Stupid question, but why is this called "memfile_notifier" and not > "memfd_notifier". We're only dealing with memfd's after all ... which > are anonymous files essentially. Or what am I missing? Are there any > other plans for fs than plain memfd support that I am not aware of? There were some discussions on this in v3. https://lkml.org/lkml/2021/12/28/484 Sean commented it's OK to abstract it from memfd but he also wants the kAPI (name) should not bind to memfd to make room for future non-memfd usages. > > > > > It will be used for KVM to use a file descriptor as the guest memory > > backing store and KVM will use this memfile_notifier interface to > > interact with memory file subsystems. In the future there might be other > > consumers (e.g. VFIO with encrypted device memory). > > > > It consists below components: > > - memfile_backing_store: Each supported memory file subsystem can be > > implemented as a memory backing store which bookmarks memory and > > provides callbacks for other kernel systems (memfile_notifier > > consumers) to interact with. > > - memfile_notifier: memfile_notifier consumers defines callbacks and > > associate them to a file using memfile_register_notifier(). > > - memfile_node: A memfile_node is associated with the file (inode) from > > the backing store and includes feature flags and a list of registered > > memfile_notifier for notifying. > > > > In KVM usages, userspace is in charge of guest memory lifecycle: it first > > allocates pages in memory backing store and then passes the fd to KVM and > > lets KVM register memory slot to memory backing store via > > memfile_register_notifier. > > Can we add documentation/description in any form how the different > functions exposed in linux/memfile_notifier.h are supposed to be used? Yeah, code comments can be added. > > Staring at memfile_node_set_flags() and memfile_notifier_invalidate() > it's not immediately clear to me who's supposed to call that and under > which conditions. I will also amend the commit message. Chao > > -- > Thanks, > > David / dhildenb
