Messages in this thread | | | Date | Tue, 25 Jan 2011 23:01:18 +0100 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 1/3] Avoid unmapping THP when it is failed to be split. |
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On Tue, Jan 25, 2011 at 02:45:27PM +0900, Jin Dongming wrote: > If the THP is failed to be split, > 1. The processes using the poisoned page could not be collected. > (Because page_mapped_in_vma() in collect_procs_anon() always > returns NULL.)
page_mapped_in_vma is only called after split_huge_page without requiring this change.
> 2. The poisoned page could not be unmapped. > (If CONFIG_DEBUG_VM is "y", VM_BUG_ON(PageTransHuge(page)) > in try_to_unmap() will be called, and system panic will be > caused.)
This is more reasonable argument for the change because at times collect_procs may fail kmalloc or for other reasons kill may be set to 1 without split_huge_page having run.
> 3. The processes using the poisoned page could not be killed, too. > (Because no process is collected in 1.)
I don't see the point of the change for 1.
> So if splitting THP is failed, it is better to stop unmapping > rather than causing panic. System might servive if the page is freed > later.
Splitting THP can't fail unless the page is freed under split_huge_page (like if the process quits while you're calling split_huge_page and in turn the anon_vma was already unusable).
Patch looks good but just for point 2.
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