On Mon, 20 Nov 2006, Jens Axboe wrote:
> On Mon, Nov 20 2006, Alan Stern wrote:
> > Paul:
> >
> > Here's my version of your patch from yesterday. It's basically the same,
> > but I cleaned up the code in a few places and fixed a bug (the sign of idx
> > in srcu_read_unlock). Also I changed the init routine back to void, since
> > it's no longer an error if the per-cpu allocation fails.
> >
> > More importantly, I added a static initializer and included the fast-path
> > in synchronize_srcu. It's protected by the new symbol
> > SMP__STORE_MB_LOAD_WORKS, which should be defined in arch-specific headers
> > for those architectures where the store-mb-load pattern is safe.
>
> Must we introduce memory allocations in srcu_read_lock()? It makes it
> much harder and nastier for me to use. I'd much prefer a failing
> init_srcu(), seems like a much better API.
Paul agrees with you that allocation failures in init_srcu() should be
passed back to the caller, and I certainly don't mind doing so.
However we can't remove the memory allocation in srcu_read_lock(). That
was the point which started this whole thread: the per-cpu allocation
cannot be done statically, and some users of a static SRCU structure can't
easily call init_srcu() early enough.
Once the allocation succeeds, the overhead in srcu_read_lock() is minimal.
Alan
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