kmap() is being deprecated in favor of kmap_local_page(). 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. 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/hfs is safe everywhere, it should be preferred. Therefore, replace kmap() with kmap_local_page() in fs/hfs. Where possible, use the suited standard helpers (memzero_page(), memcpy_page()) instead of open coding kmap_local_page() plus memset() or memcpy(). Fix a bug due to a page being not unmapped if the code jumps to the "fail_page" label (1/3). Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with HIGHMEM64GB enabled. Few days ago Andrew requested a resend of this series. In the meantime I'm also forwarding a "Reviewed-by" tag from Viacheslav Dubeyko. Fabio M. De Francesco (3): hfs: Unmap the page in the "fail_page" label hfs: Replace kmap() with kmap_local_page() in bnode.c hfs: Replace kmap() with kmap_local_page() in btree.c fs/hfs/bnode.c | 32 ++++++++++++-------------------- fs/hfs/btree.c | 29 ++++++++++++++++------------- 2 files changed, 28 insertions(+), 33 deletions(-) -- 2.37.1
