On 01/30/2013 02:29 PM, Eric W. Biederman wrote: >> >>> I think I would prefer that to call that new type RESERVED_MEM or >>> RESERVED_CACHABLE. Being more specific is fine but dumpable certainly >>> doesn't bring to mind what we are saying. Especially since we already >>> communicate which areas were memory to the last kernel in an >>> architecture generic format. >> >> I was thinking that marking them differently might help debugging, at >> least, but yes, we can have a RESERVED_MEM type. >> >> However, Thomas does have a point that the current use of fairly small >> positive values for Linux-defined types is a bad idea. We should use >> negative types, or at least something north of 0x40000000 or so. > > Yes. It doesn't much matter in the kernel but when it because part of > the ABI it is a real issue. > > Since old kernels treat any value they don't understand as reserved > passing a modified e820 map seems reasonable to me once we have reserved > a special linux value for it. > Just to prevent the possible funnies (including collisions with -errno) that might be caused by negative numbers, I suggest we assign Linux-specific values starting at some huge but still positive value like 2000000000 -- that way we avoid any possible uses of negative errno values internally in the kernel. The bigger question is if we need a separate value from the current E820_RESERVED_KERN. Since it is always easier to have multiple values with the same semantics than it is to have too few, I would still prefer we added a new E820_RESERVED_KDUMP, which would then be 2000000001. What do you think? -hpa
