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Re: COPY_DELAY could perform worse than COPY_NONE
From: |
Sergio López |
Subject: |
Re: COPY_DELAY could perform worse than COPY_NONE |
Date: |
Sat, 8 Oct 2011 01:55:42 +0200 |
More on this subject:
- MEMORY_OBJECT_COPY_DELAY is actually needed to be able to provide
private mmaps without copying the entire object at once.
- This attribute only changes the behavior of
vm_object_copy_strategically, between doing a delayed copy
(COPY_DELAY) or copying the pages for real (COPY_NONE).
- A single object can be accessed with both strategies without conflicts.
Nowadays, the copy strategy is decided per-object, but I think the
desired type of access to an object should also be considered. For
instance, the operation generated by vm_copy should almost always use
COPY_NONE, while vm_map, when doing things such as providing a private
map, should use COPY_DELAY.
I'm testing a patch which does this distinction. I'll post the results.