RE: [Linux-ia64] Fix for for memory leak in IA32 mmap

["Luck, Tony" <tony.luck@intel.com>]

> 3)  I wasn't intending to keep a bitmap for all of IA32 addressable
> memory.  I intend to keep a list of all the partial pages, basically
> the first and last page of an `mmap' request, and then keep a bitmap
> for each of the 4K chunks inside of that page.  Maintaining the bitmap
> will be a little tricky to handle all of the `mmap/munmap' possibilities
> but it shouldn't be all that hard to get it right.

Aha! A list of the partial pages makes sense. I thought that the "list" was
going to be a list of mmap'd ranges ... which would be tougher to get right
in the face of pathalogical programs.  I agree that these pathalogical
programs deserve to fail, but they shouldn't take out the system (or tie it
up with incredibly long lists of objects).

You might keep an eye on the complexity of the code for maintaining the
lists
versus just having a (2-level) bitmap for the whole of the IA-32 address
space.  There are some tricky cases (especially when you factor in support
for 64K kernel page size as well as 16K ... so your partial page bitmaps
have different lengths for different configurations).

-Tony