Re: [patch 3/6] mmu_notifier: invalidate_page callbacks

From: Avi Kivity
Date: Sat Feb 16 2008 - 14:56:17 EST


Christoph Lameter wrote:
On Fri, 15 Feb 2008, Andrew Morton wrote:

@@ -287,7 +288,8 @@ static int page_referenced_one(struct pa
if (vma->vm_flags & VM_LOCKED) {
referenced++;
*mapcount = 1; /* break early from loop */
- } else if (ptep_clear_flush_young(vma, address, pte))
+ } else if (ptep_clear_flush_young(vma, address, pte) |
+ mmu_notifier_age_page(mm, address))
referenced++;
The "|" is obviously deliberate. But no explanation is provided telling us
why we still call the callback if ptep_clear_flush_young() said the page
was recently referenced. People who read your code will want to understand
this.

Andrea?


I'm not Andrea, but the way I read it, ptep_clear_flush_young() and ->age_page() each have two effects: check whether the page has been referenced and clear the referenced bit. || would retain the semantics of the check but lose the clearing. | does the right thing.

--
Any sufficiently difficult bug is indistinguishable from a feature.

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