Re: [RFC PATCH] zram: avoid preemption with CPU-based compression backends

[Sergey Senozhatsky]

On (26/08/05 08:55), Barry Song (Xiaomi) wrote:
> Since commit 2efa9e9eb4db ("zram: permit preemption with active
> compression stream"), a major Android regression has been reported.
> 
> The reason is that compression/decompression is now sleepable and
> preemptible. This means a stream may be migrated to another CPU or
> be preempted while holding the stream mutex. As a result, high
> priority UI threads may get stuck waiting for the mutex during swap-in.
[..]
> We add an async flag (currently false for almost all backends) to
> indicate whether a backend is asynchronous. For synchronous
> backends, we use preempt_disable() in the !PREEMPT_RT case. A

I wonder what does that report say.  Is that what I think it is
(we discussed something RT related privately recently)?