[snip] > > > > For throttling case, apart from metadata, I found that with simple > > > > throttling of data I ran into issues with journalling with ext4 mounuted > > > > in ordered mode. So it was suggested that WRITE IO throttling should > > > > not be done at device level instead try to do it in higher layers, > > > > possibly balance_dirty_pages() and throttle process early. > > > > > > The problem with doing it at the page cache entry level is that > > > cache hits then get throttled. It's not really a an IO controller at > > > that point, and the impact on application performance could be huge > > > (i.e. MB/s instead of GB/s). > > > > Agreed that throttling cache hits is not a good idea. Can we determine > > if page being asked for is in cache or not and charge for IO accordingly. > > You'd need hooks in find_or_create_page(), though you have no > context of whether a read or a write is in progress at that point. I'm confused. Where is the throttling at cache hits? The balance_dirty_pages() throttling kicks in at write() syscall and page fault time. For example, generic_perform_write(), do_wp_page() and __do_fault() will explicitly call balance_dirty_pages_ratelimited() to do the write throttling. Thanks, Fengguang -- 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
