On Fri, 30 Dec 2022, Ira Weiny wrote: > 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> > > Nicolas, I was auditing the kmap conversion status and I see you reviewed this > but did not merge it. Are you still the maintainer for fs/cramfs? Should > Fabio send this to someone else? Please send it to Al Viro with my reviewed-by. Nicolas
