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    SubjectRe: [PATCH] Convert idr's internal locking to _irqsave variant
    On Thu, 13 Jul 2006 14:03:21 -0700
    Roland Dreier <rdreier@cisco.com> wrote:

    > > I suspect it'll get really ugly. It's a container library which needs to
    > > allocate memory when items are added, like the radix-tree. Either it needs
    > > to assume GFP_ATOMIC, which is bad and can easily fail or it does weird
    > > things like radix_tree_preload().
    >
    > Actually I don't think it has to be too bad. We could tweak the
    > interface a little bit so that consumers do something like:
    >
    > struct idr_layer *layer = NULL; /* opaque */
    >
    > retry:
    > spin_lock(&my_idr_lock);
    > ret = idr_get_new(&my_idr, ptr, &id, layer);
    > spin_unlock(&my_idr_lock);
    >
    > if (ret == -EAGAIN) {
    > layer = idr_alloc_layer(&my_idr, GFP_KERNEL);
    > if (!IS_ERR(layer))
    > goto retry;
    > }
    >
    > in other words make the consumer responsible for passing in new memory
    > that can be used for a new entry (or freed if other entries have
    > become free in the meantime).
    >

    Good point, a try-again loop would work. Do we really need the caller to
    maintain a cache? I suspect something like

    drat:
    if (idr_pre_get(GFP_KERNEL) == ENOMEM)
    give_up();
    spin_lock();
    ret = idr_get_new();
    spin_unlock();
    if (ret == ENOMEM)
    goto drat;

    would do it.
    -
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