Messages in this thread | | | Date | Thu, 1 Sep 2022 00:53:21 +0100 | From | Al Viro <> | Subject | Re: [PATCH v2] nvmet-tcp: Don't map pages which can't come from HIGHMEM |
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On Wed, Aug 31, 2022 at 12:05:33AM +0200, Fabio M. De Francesco wrote: > kmap() is being deprecated in favor of kmap_local_page().[1] > > There are two main problems with kmap(): (1) It comes with an overhead as > 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. > > The pages which will be mapped are allocated in nvmet_tcp_map_data(), > using the GFP_KERNEL flag. This assures that they cannot come from > HIGHMEM. This imply that a straight page_address() can replace the kmap() > of sg_page(sg) in nvmet_tcp_map_pdu_iovec(). As a side effect, we might > also delete the field "nr_mapped" from struct "nvmet_tcp_cmd" because, > after removing the kmap() calls, there would be no longer any need of it. > > In addition, there is no reason to use a kvec for the command receive > data buffers iovec, use a bio_vec instead and let iov_iter handle the > buffer mapping and data copy. > > Test with blktests on a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with > HIGHMEM64GB enabled.
Looks sane...
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