Re: [PATCH] nvmet: avoid unnecessary fsync and flush bio

[Christoph Hellwig <hch@lst.de>]

On Fri, Jul 22, 2022 at 08:12:24PM +0800, Guixin Liu wrote:
> @@ -333,10 +333,16 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
>  static void nvmet_bdev_execute_flush(struct nvmet_req *req)
>  {
>  	struct bio *bio = &req->b.inline_bio;
> +	struct request_queue *q = req->ns->bdev->bd_queue;
>  
>  	if (!nvmet_check_transfer_len(req, 0))
>  		return;
>  
> +	if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {

This should be using a bdev_write_cache.

But more importantly:  if the backend does not have a volatile write
cache, and we should not even receive flushes from the remote side.

> +	if (req->ns->buffered_io)
> +		return errno_to_nvme_status(req, vfs_fsync(req->ns->file, 1));
> +	else
> +		return errno_to_nvme_status(req, 0);

No need for the else, and the simple success case can just use the
constant status and does not need a translation.