Messages in this thread |  | | Date | Mon, 17 Oct 2016 15:00:05 +1100 | From | Nicholas Piggin <> | Subject | Re: [PATCH v2] mm: vmalloc: Replace purge_lock spinlock with atomic refcount |
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On Sat, 15 Oct 2016 03:42:42 -0700 Joel Fernandes <joelaf@google.com> wrote:
> The purge_lock spinlock causes high latencies with non RT kernel. This has been > reported multiple times on lkml [1] [2] and affects applications like audio. > > In this patch, I replace the spinlock with an atomic refcount so that > preemption is kept turned on during purge. This Ok to do since [3] builds the > lazy free list in advance and atomically retrieves the list so any instance of > purge will have its own list it is purging. Since the individual vmap area > frees are themselves protected by a lock, this is Ok.
This is a good idea, and good results, but that's not what the spinlock was for -- it was for enforcing the sync semantics.
Going this route, you'll have to audit callers to expect changed behavior and change documentation of sync parameter.
I suspect a better approach would be to instead use a mutex for this, and require that all sync=1 callers be able to sleep. I would say that most probably already can.
Thanks, Nick
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