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SubjectRe: [PATCH] Convert idr's internal locking to _irqsave variant
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Date
 > 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).

- R.
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