1c951556bc
Introduce pmap_try_insert_pv_entry(), a function that conditionally creates a pv entry if the number of entries is below the high water mark for pv entries. Introduce pmap_enter_quick_locked() and use it to reimplement pmap_enter_object(). The old implementation was broken. For example, it could block while holding a mutex lock. Change pmap_enter_quick_locked() to fail rather than wait if it is unable to allocate a page table page. This prevents a race between pmap_enter_object() and the page daemon. Specifically, an inactive page that is a successor to the page that was given to pmap_enter_quick_locked() might become a cache page while pmap_enter_quick_locked() waits and later pmap_enter_object() maps the cache page violating the invariant that cache pages are never mapped. Similarly, change pmap_enter_quick_locked() to call pmap_try_insert_pv_entry() rather than pmap_insert_entry(). Generally speaking, pmap_enter_quick_locked() is used to create speculative mappings. So, it should not try hard to allocate memory if free memory is scarce. Tested by: gonzo |
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