On Thu, Nov 22, 2007 at 01:49:25AM +0100, Andi Kleen wrote: > David Chinner <[EMAIL PROTECTED]> writes: > > > To ensure that log I/O is issued as the highest priority I/O, set > > the I/O priority of the log I/O to the highest possible. This will > > ensure that log I/O is not held up behind bulk data or other > > metadata I/O as delaying log I/O can pause the entire transaction > > subsystem. Introduce a new buffer flag to allow us to tag the log > > buffers so we can discrimiate when issuing the I/O. > > Won't that possible disturb other RT priority users that do not need > log IO (e.g. working on preallocated files)? Seems a little > dangerous.
In all the cases that I know of where ppl are using what could be considered real-time I/O (e.g. media environments where they do real-time ingest and playout from the same filesystem) the real-time ingest processes create the files and do pre-allocation before doing their I/O. This I/O can get held up behind another process that is not real time that has issued log I/O. Given there is no I/O priority inheritence and having log I/O stall will stall the entire filesystem, we cannot allow log I/O to stall in real-time environments. Hence it must have the highest possible priority to prevent this. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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/
