Messages in this thread | | | From | David Mosberger <> | Date | Thu, 23 May 2002 10:02:33 -0700 | Subject | Re: Q: PREFETCH_STRIDE/16 |
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>>>>> On Thu, 23 May 2002 09:34:16 -0700 (PDT), "David S. Miller" <davem@redhat.com> said:
DaveM> I mentioned this 1 or 2 days ago in the TLB thread with DaveM> Linus, you pessimistically maintain a tiny bitmap per DaveM> mm_struct which keeps track of where mappings actually are. DaveM> You use some hash function on the virtual address to DaveM> determine the bit. You clear it when the mm_struct is new, DaveM> and you just set bits when mappings are installed. Very DaveM> simple.
DaveM> Then all of these "walk all valid page tables" loops that DaveM> scan entire mostly empty pages of pgd/pmd/pte entries for no DaveM> reason can just check the bitmap instead.
DaveM> Most of the exit overhead is in clear_page_tables walking DaveM> over entire pages. It effectively flushes the cache unless DaveM> all you are doing is fork/exit/fork/exit
Sounds like something worth experimenting with. I doubt you could really avoid (effectively) flushing the caches, but even if there are just a few zero bits in the bitmap at the time of the tear-down, a fair amount of time could be saved.
--david - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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