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    SubjectRe: dirty balancing deadlock
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    > > > > > In general, writepage is supposed to do work without blocking on
    > > > > > expensive locks that will get pdflush and dirty reclaim stuck in this
    > > > > > fashion. You'll probably have to take the same approach reiserfs does
    > > > > > in data=journal mode, which is leaving the page dirty if fuse_get_req_wp
    > > > > > is going to block without making progress.
    > > > >
    > > > > Pdflush, and dirty reclaim set wbc->nonblocking to true.
    > > > > balance_dirty_pages and fsync don't. The problem here is that
    > > > > Andrew's patch is wrong to let balance_dirty_pages() try to write back
    > > > > pages from a different queue.
    > > >
    > > > async or sync, writepage is supposed to either make progress or bail.
    > > > loopback aside, if the fuse call is blocking long term, you're going to
    > > > run into problems.
    > >
    > > Hmm, like what?
    >
    > Something a little different from what you're seeing. Basically if the
    > PF_MEMALLOC paths end up waiting on a filesystem transaction, and that
    > transaction is waiting for more ram, the system will eventually grind to
    > a halt. data=journal is the easiest way to hit it, since writepage
    > always logs at least 4k.
    >
    > WB_SYNC_NONE and wbc->nonblocking aren't a great test, in reiser I
    > resorted to testing PF_MEMALLOC.

    I'm not pretending to understand how journaling filesystems work, but
    this shouldn't be an issue with fuse. Can you show me a call path,
    where PF_MEMALLOC is set and .nonblocking is not?

    Thanks,
    Miklos
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