One simple way to fix this would be to implement a fadvise() flag
that puts the dentry/inode on a "soon to be expired" list if there
are no other references. Then if a dentry allocation needs more
memory try to reuse dentries from that list (or better queue) first. Any other
access will remove the dentry from the list.
Disadvantage would be that the userland would need to be patched,
but I guess it's better than adding very dubious heuristics to the
kernel.
Similar thing could be done for directory buffers although they
are probably less of a problem.
I expect that C.Lameter's directed dentry/inode freeing in slub will also
make a big difference. People who have problems with updatedb should
definitely try mm which has it I believe and enable SLUB.
-Andi (who always thought swap prefetch was just a workaround, not
a real solution)
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