Re: [PATCH] fs/cramfs: Convert kmap() to kmap_local_data()

[Christian Brauner]

On Wed, Oct 12, 2022 at 11:13:56AM +0200, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page().
> 
> There are two main problems with kmap(): (1) It comes with an overhead as
> the mapping space is restricted and protected by a global lock for
> synchronization and (2) it also requires global TLB invalidation when the
> kmap’s pool wraps and it might block when the mapping space is fully
> utilized until a slot becomes available.
> 
> With kmap_local_page() the mappings are per thread, CPU local, can take
> page faults, and can be called from any context (including interrupts).
> It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
> the tasks can be preempted and, when they are scheduled to run again, the
> kernel virtual addresses are restored and still valid.
> 
> Since its use in fs/cramfs is safe everywhere, it should be preferred.
> 
> Therefore, replace kmap() with kmap_local_page() in fs/cramfs. Instead
> of open-coding kmap_local_page() + memcpy(), use memcpy_from_page().
> 
> Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@xxxxxxxxx>
> Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
> ---

Looks good to me,
Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>