linux-ext4 - Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax

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Date:	Mon, 02 May 2016 21:32:55 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Dan Williams <dan.j.williams@...el.com>
CC:	Vishal Verma <vishal.l.verma@...el.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	linux-block@...r.kernel.org, Jan Kara <jack@...e.cz>,
	Matthew Wilcox <matthew@....cx>,
	Dave Chinner <david@...morbit.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	XFS Developers <xfs@....sgi.com>, Jens Axboe <axboe@...com>,
	Linux MM <linux-mm@...ck.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io

On 05/02/2016 09:10 PM, Dan Williams wrote:
<>
> 
> The semantic I am talking about preserving is:
> 
> buffered / unaligned write of a bad sector => -EIO on reading into the
> page cache
> 

What about aligned buffered write? like write 0-to-eof
This still broken? (and is what restore apps do)

> ...and that the only guaranteed way to clear an error (assuming the
> block device supports it) is an O_DIRECT write.
> 

Sure fixing dax_do_io will guaranty that.

<>
> I still think we're talking past each other on this point.  

Yes we are!

> This patch
> set is not overloading error semantics, it's fixing the error handling
> problem that was introduced in this commit:
> 
>    d475c6346a38 dax,ext2: replace XIP read and write with DAX I/O
> 
> ...where we started overloading O_DIRECT and dax_do_io() semantics.
> 

But above does not fix them does it? it just completely NULLs DAX for
O_DIRECT which is a great pity, why did we do all this work in the first
place.

And then it keeps broken the aligned buffered writes, which are still
broken after this set.

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.
Do you need that I send you a patch to demonstrate what I mean?

But yes I feel too that "we're talking past each other". I did want
to come to LSF and talk to you, but was not invited. Should I call you?

Thanks
Boaz

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