Messages in this thread | | | Date | Mon, 20 Jun 2005 07:30:10 -0400 | From | Mauricio Lin <> | Subject | Re: How to identify cow (copy-on-write) pages during kernel execution? |
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Hi,
On 6/20/05, Carsten Otte <cotte.de@gmail.com> wrote: > On 6/20/05, Mauricio Lin <mauriciolin@gmail.com> wrote: > > I would like to know if there is a way to identify > > struct page that is cow (copy-on-write). > > > > The way I figured out to identify cow pages is when > > copy-on-write happens. I mean I identify cow pages > > inside the do_wp_page(), the function that handles > > copy-on-write. I have checked do_no_page() as well. > > > > I have included a field (is_cow) in the struct page to > > identify cow page. > > > > struct page { > > ... > > atomic_t is_cow; > > } > > > > But I wonder if it is possible to identify cow pages > > before copy-on-write happens. So identify cow pages in > > advance before any process tries to write to a cow > > page. > > > > I have checked the do_fork(), copy_process() and > > copy_mm() function to try to identify cow pages during > > the process creation, but no success. In copy_mm(), > > just the mm (of current process) is provided to the > > child process, but there are no references to struct > > pages related to mm and its VMAs. > > > > So when a page struct is considered a cow in the > > kernel and its count variable is updated? Certainly > > the counter page (page->_count) is updated when a page > > is shared because of copy-on-write feature. > > How can I identify cow pages when it becomes cow? Is > > there any feasible way to perform that? > Franky, one cannot predict which pages will get copied on > write since that is related to the behaviour of the process: > if the process writes, then the corresponding page gets copied. > If the vma has the VM_WRITE flag set, and the pte is read-only, > the page is a candidate to become subject to copy on write.
So the only way to identify copy-on-write pages is when page fault related to copy-on-write happens, right? I mean in the handle_pte_fault() that calls do_wp_page().
BR,
Mauricio Lin. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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