On Wed, Jul 20, 2022 at 06:19:32PM +0200, Fabio M. De Francesco wrote: > kmap() is being deprecated in favor of kmap_local_page(). > > 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). > Tasks can be preempted and, when scheduled to run again, the kernel > virtual addresses are restored and still valid. > > kmap_local_page() is faster than kmap() in kernels with HIGHMEM enabled. > > Since the use of kmap_local_page() in module_gzip_decompress() and in > module_xz_decompress() is safe (i.e., it does not break the strict rules > of use), it should be preferred over kmap(). > > Therefore, replace kmap() with kmap_local_page(). > > Tested on a QEMU/KVM x86_32 VM with 4GB RAM, booting kernels with > HIGHMEM64GB enabled. Modules compressed with XZ or GZIP decompress > properly. > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> Thanks for the enhanced commit log! Queued onto modules-testing, if that doesn't blow something up I'll move to modules-next afterwards. Luis
