On Tue, Apr 07 2009, Theodore Tso wrote: > On Tue, Apr 07, 2009 at 09:32:39PM +0200, Jens Axboe wrote: > > > > This should be all you need, forget the below. The manual unplugging > > only really makes sense for very select situations, since it'll be done > > when someone waits on the buffer anyway. > > Thanks, ok; I missed the "sync_buffer" in the call to wait_on_bit() in > __wait_on_buffer(). It also wasn't obvious to me that > wait_on_writeback_range() ultimately ends up calling aops->sync_page > which for filemap.c will call blk_run_backing_dev() --- and that > blk_run_*() results in the right device queue getting unplugged. So > this would be a nice thing to get documented in > Documentation/biodoc.txt. I'm not even sure what is documented about this sort of thing in biodoc, but it's actually somewhat outside the realm of block layer documentation. The block layer should document that you need to call unplug if you are going to be waiting for that IO. How the vm code does it is implementation detail mostly, the important thing is that it gets done :-) -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
