Re: [PATCH v8 15/18] mm, fs, dax: handle layout changes to pinned dax mappings

[Dan Williams]

On Mon, Apr 9, 2018 at 9:49 AM, Jan Kara <jack@xxxxxxx> wrote:
> On Sat 07-04-18 12:38:24, Dan Williams wrote:
[..]
>> I wonder if this can be trivially solved by using srcu. I.e. we don't
>> need to wait for a global quiescent state, just a
>> get_user_pages_fast() quiescent state. ...or is that an abuse of the
>> srcu api?
>
> Well, I'd rather use the percpu rwsemaphore (linux/percpu-rwsem.h) than
> SRCU. It is a more-or-less standard locking mechanism rather than relying
> on implementation properties of SRCU which is a data structure protection
> method. And the overhead of percpu rwsemaphore for your use case should be
> about the same as that of SRCU.

I was just about to ask that. Yes, it seems they would share similar
properties and it would be better to use the explicit implementation
rather than a side effect of srcu.