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    SubjectRe: Issues with using fanotify for a filesystem indexer
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    On Thu, 2009-04-02 at 18:50 +0200, Jan Kara wrote:
    > On Thu 02-04-09 18:29:04, Alexander Larsson wrote:
    > > Another potential issue with this is that every change bubbles up to the
    > > top, modifying the recursive mtime of that. This will become very
    > > contented, and may imply a partial serialization of fs activity, which
    > > is kinda costly.
    > Not every change - only the first change bubbles to the top, clearing the
    > flag on its way. Then next change stops bubbling up as soon as it reaches
    > a directory with the flag cleared. So no contention happen - we update flag
    > + timestamp only at most once per scan of the directory by indexer (or
    > someone else interested in recursive mtime) => once per a few minutes on
    > average system.

    Ah, I see. The indexer sets the flag.
    I see some issues. First of all, writing the flag/mtime to disk seems
    like a bad idea. It'll cause a lot of writing when the indexer recurses
    throught the filesystem, similar to atimes. But, if you're not
    persisting the flag/mtime then you need to keep all the dentries with
    the flag set in memory, which has resource use risks similar to
    unbounded event queues.




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