On Mon, 13 Jul 2020 at 16:06, Christoph Hellwig <h...@infradead.org> wrote: > > On Fri, Jul 10, 2020 at 08:55:42PM -0700, Palmer Dabbelt wrote: > > +ssize_t copy_oldmem_page(unsigned long pfn, char *buf, > > + size_t csize, unsigned long offset, > > + int userbuf) > > +{ > > + void *vaddr; > > + > > + if (!csize) > > + return 0; > > + > > + vaddr = memremap(__pfn_to_phys(pfn), PAGE_SIZE, MEMREMAP_WB); > > + if (!vaddr) > > + return -ENOMEM; > > Doing a memremap for every page is very inefficient.
memremap(MEMREMAP_WB) will reuse the existing linear address if the PA is covered by the linear mapping. > Also I don't see > why you'd want to even do that. All memory is in the direct mapping > for RISC-V. For other architecture that support highmem kmap_atomic_pfn > would do the job, which is what I'd use in a generic version.