From: Boaz Harrosh <boaz@plexistor.com>
Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io
Date: Mon, 02 May 2016 22:22:10 +0300
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Cc: Vishal Verma <vishal.l.verma@intel.com>,
 "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
 linux-block@vger.kernel.org, Jan Kara <jack@suse.cz>,
 Matthew Wilcox <matthew@wil.cx>,
 Dave Chinner <david@fromorbit.com>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 XFS Developers <xfs@oss.sgi.com>, Jens Axboe <axboe@fb.com>,
 Linux MM <linux-mm@kvack.org>,
 Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@infradead.org>,
 linux-fsdevel <linux-fsdevel@vger.kernel.org>,
 Andrew Morton <akpm@linux-foundation.org>,
 linux-ext4 <linux-ext4@vger.kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
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On 05/02/2016 09:48 PM, Dan Williams wrote:
<>
>> And then it keeps broken the aligned buffered writes, which are still
>> broken after this set.
> 
> ...identical to the current situation with a traditional disk.
> 

Not true!! please see what I wrote "aligned buffered writes"
If there are no reads involved then there are no errors returned
to application.

>> I have by now read the v2 patches. And I think you guys did not yet try
>> the proper fix for dax_do_io. I think you need to go deeper into the loops
>> and selectively call bdev_* when error on a specific page copy. No need to
>> go through direct_IO path at all.
> 
> We still reach a point where the minimum granularity of
> bdev_direct_access() is larger than a sector, so you end up still
> needing to have the application understand how to send a properly
> aligned I/O.  The semantics of how to send a properly aligned
> direct-I/O are already well understood, so we simply reuse that path.
> 

You are making a mountain out of a mouse. The simple copy of a file
from start (offset ZERO) to end-of-file which is the most common usage
on earth is perfectly aligned and needs not any O_DIRECT and is what is used
everywhere.

>> Do you need that I send you a patch to demonstrate what I mean?
> 
> I remain skeptical of what you are proposing, but yes, a patch has a
> better chance to move the discussion forward.
> 

Sigh! OK
Boaz

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