x86, kdump: Change copy_oldmem_page() to use cached addressing

The copy of /proc/vmcore to a user buffer proceeds much faster
if the kernel addresses memory as cached.

With this patch we have seen an increase in transfer rate from
less than 15MB/s to 80-460MB/s, depending on size of the
transfer. This makes a big difference in time needed to save a
system dump.

Signed-off-by: Cliff Wickman <[email protected]>
Acked-by: "Eric W. Biederman" <[email protected]>
Cc: [email protected]
Cc: <[email protected]> # as far back as it would apply
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

Author: cpwickman

arch/x86/kernel/crash_dump_64.c

@@ -34,7 +34,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!csize)
 		return 0;
 
-	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
+	vaddr = ioremap_cache(pfn << PAGE_SHIFT, PAGE_SIZE);
 	if (!vaddr)
 		return -ENOMEM;