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    SubjectRe: [PATCH] CacheFS - general filesystem cache
    Date

    Troy Benjegerdes <hozer@hozed.org> wrote:
    > So is it even remotely feasable to be able to use a cachefs filesystem
    > when the 'backing store' (say NFSv4) filesystem is not accessible?

    Well, in cachefs's current state:

    (1) That's mostly netfs policy. CacheFS is mainly for serving pages to the
    netfs upon demand. The netfs has to create a cachefs index tree suitable
    for it to be able to find its files. I'm currently arranging things in my
    AFS client and in the NFS client such that these correspond to server
    concepts such as cell address, volume ID, file ID; server IP address,
    file handle. I'm not arranging things as directories and
    files.

    (2) The user can just add or remove caches with mount/umount, even when live;
    so you could find that your inodes that were being backed in the cache
    are suddenly unavailable. Caches could be locked in the mount tree as
    long as a netfs is using them for disconnected mode operation.

    (3) CacheFS does not enforce any complete-file reading which you'd require to
    have disconnected operation. It only cares about pages. This is netfs
    policy.

    (4) CacheFS does not provide pinning facilities, other than active cache
    inodes don't get eaten because there's too little space and we need to
    recycle something.

    I'm planning on adding pinning facilities for use with kAFS. I'd like to add
    simple disconnected operation facilities too.

    >
    > Obviously if the file's not already cached, you lose.

    The file, and potentially the nest of directories in which it resides.

    David
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