On Tue 09-11-10 16:15:52, Rik van Riel wrote: > On 11/09/2010 04:07 PM, Ted Ts'o wrote: > >On Tue, Nov 09, 2010 at 02:33:29PM -0500, Rik van Riel wrote: > >> > >>There are essentially two possibilities: > >>1) the VM can potentially be filled up with uncleanable dirty pages, or > >>2) pages that hit an IO error are left in a clean state, so they can > >> be reclaimed under memory pressure > >> > >>Alternative 1 could cause the entire system to deadlock, while > >>option 2 puts the onus on userland apps to rewrite the data > >>from a failed msync/fsync. > >> > >>Currently the VM has behaviour #2 which is preserved with my > >>patch. > >> > >>The only difference with my patch is, we won't keep returning > >>-EIO on subsequent, error free, msync or fsync calls to files > >>that had an IO error at some previous point in the past. > > > >Do we guarantee that the application will get EIO at least once? I > >thought there were issues where the error bit could get lost if the > >page writeback was triggered by sync() run by a third-party > >application. > > There is no such guarantee in the current kernel, either > with or without my patch. > > A third application calling fsync or msync can get the > EIO cleared, so the application that did the write does > not see it. > > The VM could also reclaim the PageError page due to > memory pressure, so the application calling fsync or > msync does not see it. What should be done in this case is that we set AS_EIO in the page->mapping->flags like we currently do in fs/buffer.c. > I see no good way in which we could guarantee that > every process calling msync or fsync on a file that > had an IO error in the past gets EIO once - at least, > not without every one of them always getting EIO on > the file even after the IO path is good again... Yes, this is rather hard to do... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
