On Tue, Nov 1, 2011 at 4:10 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Tue, Nov 1, 2011 at 4:03 PM, Jan Kara <jack@xxxxxxx> wrote: >> >> Avoiding IO during a minor fault would be a decent thing which might be >> worth pursuing. As you properly noted "stable pages during writeback" >> requirement is one obstacle which won't be that trivial to avoid though... > > There's an easy solution that would be good enough for me: add a mount > option to turn off stable pages. > > Is the other problem just a race, perhaps? __block_page_mkwrite calls > __block_write_begin (which calls get_block, which I think is where the > latency comes from) *before* wait_on_page_writeback, which means that > there might not be any space allocated yet. I think I'm right (other than calling it a race). If I change my code to do: - map the file (with MCL_FUTURE set) - fallocate - dirty all pages - fsync - dirty all pages again in the non-real-time thread, then a short test that was a mediocre reproducer seems to work. This is annoying, though -- I'm not generating twice as much write I/O as I used to. Is there any way to force the delalloc code to do its thing without triggering writeback? I don't think fallocate has this effect. --Andy -- 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
