linux-kernel - Re: [PATCH v5] DAX: enable iostat for read/write

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Date:   Thu, 12 Jan 2017 10:02:21 -0800
From:   Joe Perches <joe@...ches.com>
To:     Toshi Kani <toshi.kani@....com>, akpm@...ux-foundation.org,
        dan.j.williams@...el.com
Cc:     david@...morbit.com, viro@...iv.linux.org.uk,
        ross.zwisler@...ux.intel.com, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] DAX: enable iostat for read/write

On Thu, 2017-01-12 at 11:38 -0700, Toshi Kani wrote:
> DAX IO path does not support iostat, but its metadata IO path does.
> Therefore, iostat shows metadata IO statistics only, which has been
> confusing to users.
[]
> diff --git a/fs/dax.c b/fs/dax.c
[]
> @@ -1058,12 +1058,24 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
>  {
>  	struct address_space *mapping = iocb->ki_filp->f_mapping;
>  	struct inode *inode = mapping->host;
> +	struct gendisk *disk = inode->i_sb->s_bdev->bd_disk;
>  	loff_t pos = iocb->ki_pos, ret = 0, done = 0;
>  	unsigned flags = 0;
> +	unsigned long start = 0;
> +	int do_acct = blk_queue_io_stat(disk->queue);
>  
>  	if (iov_iter_rw(iter) == WRITE)
>  		flags |= IOMAP_WRITE;
>  
> +	if (do_acct) {
> +		sector_t sec = iov_iter_count(iter) >> 9;
> +
> +		start = jiffies;
> +		generic_start_io_acct(iov_iter_rw(iter),
> +				      min_t(unsigned long, 1, sec),

I believe I mislead you with a thinko.

Your original code was
	(!sec) ? 1 : sec
and I suggested incorrectly using min_t

It should of course be max_t.  Sorry.

Also, as sec is now sector_t (u64), perhaps this
unsigned long cast is incorrect.