On Wed, May 16, 2007 at 06:21:09PM +0100, Hugh Dickins wrote: > On Sun, 13 May 2007, Nick Piggin wrote: > > On Fri, May 11, 2007 at 02:15:03PM +0100, Hugh Dickins wrote: > > > > > But again I wonder just what the gain has been, once your double > > > unmap_mapping_range is factored in. When I suggested before that > > > perhaps the double (well, treble including the one in truncate.c) > > > unmap_mapping_range might solve the problem you set out to solve > > > (I've lost sight of that!) without pagelock when faulting, you said: > > > > > > > Well aside from being terribly ugly, it means we can still drop > > > > the dirty bit where we'd otherwise rather not, so I don't think > > > > we can do that. > > > > > > but that didn't give me enough information to agree or disagree. > > > > Oh, well invalidate wants to be able to skip dirty pages or have the > > filesystem do something special with them first. Once you have taken > > the page out of the pagecache but still mapped shared, then blowing > > it away doesn't actually solve the data loss problem... only makes > > the window of VM inconsistency smaller. > > Right, I think I see what you mean now, thanks: userspace > must not for a moment be allowed to write to orphaned pages.
Yep. > Whereas it's not an issue for the privately COWed pages you added > the second unmap_mapping_range for: because it's only truncation > that has to worry about them, so they're heading for SIGBUS anyway. > > Yes, and the page_mapped tests in mm/truncate.c are just racy > heuristics without the page lock you now put into faulting. Yes. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
