Dave Chinner <david@xxxxxxxxxxxxx> writes: > On Tue, Apr 07, 2015 at 02:55:13PM -0400, Jeff Moyer wrote: >> The way the on-stack plugging currently works, each nesting level >> flushes its own list of I/Os. This can be less than optimal (read >> awful) for certain workloads. For example, consider an application >> that issues asynchronous O_DIRECT I/Os. It can send down a bunch of >> I/Os together in a single io_submit call, only to have each of them >> dispatched individually down in the bowels of the dirct I/O code. >> The reason is that there are blk_plug-s instantiated both at the upper >> call site in do_io_submit and down in do_direct_IO. The latter will >> submit as little as 1 I/O at a time (if you have a small enough I/O >> size) instead of performing the batching that the plugging >> infrastructure is supposed to provide. > > I'm wondering what impact this will have on filesystem metadata IO > that needs to be issued immediately. e.g. we are doing writeback, so > there is a high level plug in place and we need to page in btree > blocks to do extent allocation. We do readahead at this point, > but it looks like this change will prevent the readahead from being > issued by the unplug in xfs_buf_iosubmit(). I'm not ignoring you, Dave, I'm just doing some more investigation and testing. It's taking longer than I had hoped. -Jeff -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>