On Fri, Jun 17, 2011 at 5:55 PM, Petr Tesarik <ptesarik@xxxxxxx> wrote: > Dne Pá 17. června 2011 11:30:32 Ingo Molnar napsal(a): >> * Petr Tesarik <ptesarik@xxxxxxx> wrote: >> > This patch series enhances /dev/mem, so that read and write is >> > possible at any address. The patchset includes actual >> > implementation for x86. >> >> This series lacks a description of why this is desired. > > Hi Ingo, > >> My strong opinion is that it's not desired at all: /dev/mem never >> worked beyond 4G addresses so by today it has become largely obsolete >> and is on the way out really. >> >> I'm aware of these current /dev/mem uses: >> >> - Xorg maps below 4G non-RAM addresses and the video BIOS >> >> - It used to have some debugging role but these days kexec and kgdb >> has largely taken over that role - partly due to the 4G limit. > > It is still used as a "memory source" by Dave Anderson's crash utility for > live examination of a running system. Redhat has "overcome" the /dev/mem > deficiencies by writing an out-of-tree re-implementation of /dev/mem, which > uses /dev/crash instead. As it is an "unnecessary duplication of an existing > driver", this method was rejected by the project manager here at SUSE. > > The suggested alternative was to enhance (or fix) the existing driver. Without > this patch series there is no way to access high memory. In conjunction with > CONFIG_HIGHPTE, it makes the crash utility near to useless on anything with > high memory, because crash can no longer translate virtual to physical > addresses. > How about /proc/kcore? AFAIK, it can access highmem, but Dave didn't consider it for some reason. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html