On Thu, May 7, 2015 at 3:24 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> @@ -441,6 +500,12 @@ static void do_loop_switch(struct loop_device *lo, struct switch_request *p) >> mapping->host->i_bdev->bd_block_size : PAGE_SIZE; >> lo->old_gfp_mask = mapping_gfp_mask(mapping); >> mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS)); >> + >> + lo->support_dio = mapping->a_ops && mapping->a_ops->direct_IO; >> + if (lo->support_dio) >> + lo->use_aio = true; >> + else >> + lo->use_aio = false; > > We need an explicit userspace op-in for this. For one direct I/O can't Actually this patch is one simplified version, and my old version has exported two sysfs files(use_aio, use_dio) which can control if direct IO or AIO is used but only AIO is enabled if DIO is set. Finally I think it isn't necessary because dio/aio works well from the tests, and userspace shouldn't care if it is AIO or not if the performance is good. > handle sub-sector size access and people use the loop device as a > workaround for that. Yes, user can do that, could you explain a bit what the problem is? > Second this doesn't give anyone seeing negative > results from aio a way to disable it easily. If there is the requirement, we can export the control interface via sysfs files easily, but I suggest to not do that from the start for sake of simplicity. > > It think the best way is to require a setup time flag, but enable it to > on in losetup versions that know about it. Could you explain a bit why we need losetup involved? > >> @@ -761,6 +826,13 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, >> if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync) >> blk_queue_flush(lo->lo_queue, REQ_FLUSH); >> >> + /* use aio if it is possible */ >> + lo->support_dio = mapping->a_ops && mapping->a_ops->direct_IO; >> + if (lo->support_dio) >> + lo->use_aio = true; >> + else >> + lo->use_aio = false; > > Please always factor out checks like this insted of duplicating them. OK, will do that. Thanks, Ming -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
