On Tue, Jun 08, 2010 at 03:38:31PM +1000, Nick Piggin wrote: > On Tue, Jun 08, 2010 at 10:38:07AM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > sync can currently take a really long time if a concurrent writer is > > extending a file. The problem is that the dirty pages on the address > > space grow in the same direction as write_cache_pages scans, so if > > the writer keeps ahead of writeback, the writeback will not > > terminate until the writer stops adding dirty pages. > > > > For a data integrity sync, we only need to write the pages dirty at > > the time we start the writeback, so we can stop scanning once we get > > to the page that was at the end of the file at the time the scan > > started. > > > > This will prevent operations like copying a large file preventing > > sync from completing as it will not write back pages that were > > dirtied after the sync was started. This does not impact the > > existing integrity guarantees, as any dirty page (old or new) > > within the EOF range at the start of the scan will still be > > captured. > > > > This patch will not prevent sync from blocking on large writes into > > holes. > > The writes don't have to be into holes to cause this starvation > problem, do they? No, they don't. > > That requires more complex intervention while this patch only > > addresses the common append-case of this sync holdoff. > > Jan's tagging patch looks pretty good to me and isn't so complex. > I think we should just take that. I don't care which one we take as long as it is actually tested by more than the submitter and we get everything in for 2.6.35... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
