If highmem is enabled, 32 MB at the top of the address space is reserved 
for kmap. This is not necessary: the kmap area is at most 4 MB long, 
reserving 8 MB is sufficient (the last few kB are needed for the 
fixmaps, and the kmap area must be 4 MB-aligned). Recovering these 24 MB 
is important - it's increases the size of the vmalloc pool.
2.6 contains a similar patch.
The patch also adds a safety check to detect a collision between fixmap 
and kmap mappings - just in case someone uses huge fixmaps.

Marcelo, could you add it to your tree?

--
    Manfred