I am trying to optimize a malloc-based benchmark that is mmapping
anonymous memory (via mmap) and then eventually taking a page fault on
every page that was allocated. This is pretty inefficient for two reasons:
1) Lots of page faults, which drop performance by a factor of 10
compared to the case where everything is faulted in.
2) Lack of concurrency when faulting from multiple threads on the same
object (it is basically serialized, so no benefits from multiple CPUs)
I think a better way to go might be to do prefetching to reduce the
number of page faults. We do this for other types of mappings, but
apparently not for anonymous mmapped memory. I am still trying to get
my head around the code here, but it looks like vm_fault_prefault is
going to return without doing anything because of
while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
...
/*
* give-up when a page is not in memory
*/
Also vm_fault_additional_pages() isn't getting called because TRYPAGER
returns false for default objects.
Is there a way to achieve this that I am overlooking? If not can
someone give me some advice about what is needed?
Kris
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