Two things to both of you respectively.
Why should we try to stay out of the pte slab? Isn't the slab exactly
made for this thing? To efficiently handle a large number of equal
size objects for quick allocation and dealocation? If it is a locking
problem then there should be a per cpu cache of ptes. Say 0-32
ptes. If you run out you allocate 16 from slab. When you overflow you
free 16 (which would give you your 64k allocations but in multiple
objects).
As for the wastage. Every pte can map 2MB on amd64, 4MB on i386, 8MB
on sparc (?). A 64k pte chunk would be 32MB, 64MB and 32MB (?)
respectively. For the sbrk() and mmap() usage from glibc malloc() that
would be fine as they grow linear and the mmap() call in glibc could
be made to align to those chunks. But for a programm like rtorrent
using mmap to bring in chunks of a 4GB file this looks desasterous.
Personally I would really go with a per cpu cache. When mapping a page
reserve 4 tables. Then you walk the tree and add entries as
needed. And last you release 0-4 unused entries to the cache.
MfG
Goswin
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