linux-kernel - Re: [PATCH v6] DAX: enable iostat for read/write

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Date:   Fri, 13 Jan 2017 15:16:35 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Kani, Toshimitsu" <toshi.kani@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "joe@...ches.com" <joe@...ches.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
        "david@...morbit.com" <david@...morbit.com>
Subject: Re: [PATCH v6] DAX: enable iostat for read/write

On Fri, 13 Jan 2017 23:09:58 +0000 "Kani, Toshimitsu" <toshi.kani@....com> wrote:

> On Fri, 2017-01-13 at 14:54 -0800, Andrew Morton wrote:
> > On Fri, 13 Jan 2017 16:34:18 -0700 Toshi Kani <toshi.kani@....com>
> > 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.
> > > 
> > > Add iostat support to the DAX read/write path.
> > > 
> > > Note, iostat still does not support the DAX mmap path as it allows
> > > user applications to access directly.
> > > 
> > > ...
> > > 
> > > --- 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);
> > 
> > (The poorly named) blk_queue_io_stat() actually returns a bool.____This
> > is well concealed because blk_queue_io_stat() is unnecessarily
> > implemented as a macro (why oh why).
> 
> It was unclear to me what type I needed to use.  test_bit() is 'bool'
> in arch/x86/include/asm/bitops.h but is 'int' in  include/asm-
> generic/bitops/non-atomic.h.  So, I used 'int' for safe... 

Yes, x86 does appear to be an outlier.  Mess.