DaveM> All of these particular prefetches are amusing, with or
DaveM> without your fix, considering there are other more powerful
DaveM> ways to optimize this stuff. :-)
What do you have in mind?
I mentioned this 1 or 2 days ago in the TLB thread with
Linus, you pessimistically maintain a tiny bitmap per
mm_struct which keeps track of where mappings actually
are. You use some hash function on the virtual address
to determine the bit. You clear it when the mm_struct is
new, and you just set bits when mappings are installed.
Then all of these "walk all valid page tables" loops that scan entire
mostly empty pages of pgd/pmd/pte entries for no reason can just check
the bitmap instead.
Most of the exit overhead is in clear_page_tables walking over entire
pages. It effectively flushes the cache unless all you are doing is
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