Messages in this thread | | | Subject | Re: [patch 5/5] Optimize page_mkclean_one | From | Miklos Szeredi <> | Date | Sun, 01 Jul 2007 12:29:19 +0200 |
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> page_mkclean_one is used to clear the dirty bit and to set the write > protect bit of a pte. In additions it returns true if the pte either > has been dirty or if it has been writable. As far as I can see the > function should return true only if the pte has been dirty, or page > writeback will needlessly write a clean page.
There are some weird cases, like for example get_user_pages(), when the pte takes a write fault and the page is modified, but the pte doesn't become dirty, because the page is written through the kernel mapping.
In the get_user_pages() case the page itself is dirtied, so your patch probably doesn't break that. But I'm not sure if there aren't similar cases like that that the pte_write() check is taking care of.
And anyway if the dirty page tracking works correctly, your patch won't optimize anything, since the pte will _only_ become writable if the page was dirtied.
So in fact normally pte_dirty() and pte_write() should be equivalent, except for some weird cases.
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