On Sun, 2011-01-23 at 18:05 +0000, Russell King - ARM Linux wrote: > On Thu, Jan 20, 2011 at 10:11:27AM -0800, Dave Hansen wrote: > > On Thu, 2011-01-20 at 18:01 +0000, Russell King - ARM Linux wrote: > > > > The x86 version of show_mem() actually manages to do this without any > > > > #ifdefs, and works for a ton of configuration options. It uses > > > > pfn_valid() to tell whether it can touch a given pfn. > > > > > > x86 memory layout tends to be very simple as it expects memory to > > > start at the beginning of every region described by a pgdat and extend > > > in one contiguous block. I wish ARM was that simple. > > > > x86 memory layouts can be pretty funky and have been that way for a long > > time. That's why we *have* to handle holes in x86's show_mem(). My > > laptop even has a ~1GB hole in its ZONE_DMA32: > > If x86 is soo funky, I suggest you try the x86 version of show_mem() > on an ARM platform with memory holes. Make sure you try it with > sparsemem as well... x86 uses the generic lib/ show_mem(). It works for any holes, as long as they're expressed in one of the memory models so that pfn_valid() notices them. ARM looks like its pfn_valid() is backed up by searching the (ASM arch-specific) memblocks. That looks like it would be fairly slow compared to the other pfn_valid() implementations and I can see why it's being avoided in show_mem(). Maybe we should add either the MAX_ORDER or section_nr() trick to the lib/ implementation. I bet that would use pfn_valid() rarely enough to meet any performance concerns. -- Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>