Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 11 Jan 2023 02:25:35 +0000 | From | Al Viro <> | Subject | Re: [RESEND PATCH] fs/cramfs: Convert kmap() to kmap_local_data() |
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On Mon, Jan 09, 2023 at 07:28:43PM +0100, 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().
Applied (#work.misc).
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