Re: [PATCH v8 1/9] dax: Use percpu rwsem for dax_{read,write}_lock()

[Shiyang Ruan]

在 2021/12/14 23:40, Christoph Hellwig 写道:
> On Thu, Dec 02, 2021 at 04:48:48PM +0800, Shiyang Ruan wrote:
> > In order to introduce dax holder registration, we need a write lock for
> > dax.  Change the current lock to percpu_rw_semaphore and introduce a
> > write lock for registration.
>
> Why do we need to change the existing, global locking for that?

I think we have talked about this in the previous v7 patchset:


https://lore.kernel.org/nvdimm/20210924130959.2695749-1-ruansy.fnst@xxxxxxxxxxx/T/#m4031bc3dc49dcbaac6f8d99877f910fa9a6f998a

If it is a global lock, any write lock will block other dax devices.

> What is the impact of this to benchmarks?  Also if we stop using srcu
> protection, we should be able to get rid of grace periods or RCU frees.

I didn't test in benchmarks for now.  Could you show me which one I 
should test this code on?  I am not familiar with this...


--
Thanks,
Ruan.