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    SubjectRe: [PATCH v7 03/14] mm: Introduce memfile_notifier
    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?

    >
    > 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?

    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.

    --
    Thanks,

    David / dhildenb

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