On Fri, Oct 26, 2012 at 04:07:44PM +0200, Peter Zijlstra wrote: > On Fri, 2012-10-26 at 16:57 +0300, Kirill A. Shutemov wrote: > > > > Yes, this code will catch it: > > > > > > > > /* if an huge pmd materialized from under us just retry later */ > > > > if (unlikely(pmd_trans_huge(*pmd))) > > > > return 0; > > > > > > > > If the pmd is under splitting it's still a pmd_trans_huge(). > > > > > > OK, so then we simply keep taking the same fault until the split is > > > complete? Wouldn't it be better to wait for it instead of spin on > > > faults? > > > > IIUC, on next fault we will wait split the page in fallow_page(). > > What follow_page()?, a regular hardware page-fault will not call > follow_page() afaict, we do a down_read(), find_vma() and call > handle_mm_fault() -- with a lot of error and corner case checking in > between.
Yeah, you're right. Then, it seems we're spinning on the fault until the page is splitted. I'm not sure how long spliting takes and if splitting itself can fix some fault reason. -- Kirill A. Shutemov
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