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09132ba6ac
several reasons for this change: pmap_change_wiring() has never (in my memory) been used to set the wired attribute on a virtual page. We have always used pmap_enter() to do that. Moreover, it is not really safe to use pmap_change_wiring() to set the wired attribute on a virtual page. The description of pmap_change_wiring() says that it assumes the existence of a mapping in the pmap. However, non-wired mappings may be reclaimed by the pmap at any time. (See pmap_collect().) Many implementations of pmap_change_wiring() will crash if the mapping does not exist. pmap_unwire() accepts a range of virtual addresses, whereas pmap_change_wiring() acts upon a single virtual page. Since we are typically unwiring a range of virtual addresses, pmap_unwire() will be more efficient. Moreover, pmap_unwire() allows us to unwire superpage mappings. Previously, we were forced to demote the superpage mapping, because pmap_change_wiring() only allowed us to express the unwiring of a single base page mapping at a time. This added to the overhead of unwiring for large ranges of addresses, including the implicit unwiring that occurs at process termination. Implementations for arm and powerpc will follow. Discussed with: jeff, marcel Reviewed by: kib Sponsored by: EMC / Isilon Storage Division |
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