[PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore

H. Peter Anvin hpa at zytor.com
Thu May 16 20:06:01 EDT 2013

On 05/15/2013 02:05 AM, HATAYAMA Daisuke wrote:
> Currently, read to /proc/vmcore is done by read_oldmem() that uses
> ioremap/iounmap per a single page. For example, if memory is 1GB,
> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
> times. This causes big performance degradation.

read_oldmem() is fundamentally broken and unsafe.  It needs to be
unified with the plain /dev/mem code and any missing functionality fixed
instead of "let's just do a whole new driver".


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