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SubjectRe: [PATCH v8 1/9] dax: Use percpu rwsem for dax_{read,write}_lock()
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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@fujitsu.com/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.


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