Re: Another approach of UFSHPB

[Bart Van Assche]

On 2020-05-25 23:15, Avri Altman wrote:
>> On 2020-05-24 22:40, Daejun Park wrote:
>>> The HPB driver is close to the UFS core function, but it is not essential
>>> for operating UFS device. With reference to this article
>>> (https://lwn.net/Articles/645810/), we implemented extended UFS-feature
>>> as bus model. Because the HPB driver consumes the user's main memory, it
>> should
>>> support bind / unbind functionality as needed. We implemented the HPB
>> driver
>>> can be unbind / unload on runtime.
>>
>> I do not agree that the bus model is the best choice for freeing cache
>> memory if it is no longer needed. A shrinker is probably a much better
>> choice because the callback functions in a shrinker get invoked when a
>> system is under memory pressure. See also register_shrinker(),
>> unregister_shrinker() and struct shrinker in include/linux/shrinker.h.
>
> Since this discussion is closely related to cache allocation,
> What is your opinion about allocating the pages dynamically as the regions
> Are being activated/deactivated, in oppose of how it is done today - 
> Statically on init for the entire max-active-subregions?

Memory that is statically allocated cannot be used for any other purpose
(e.g. page cache) without triggering the associated shrinker. As far as
I know shrinkers are only triggered when (close to) out of memory. So
dynamically allocating memory as needed is probably a better strategy
than statically allocating the entire region at initialization time.

Thanks,

Bart.