linux-ext4 - Re: [PATCH v6 4/7] dax: add support for fsync/msync

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Date:	Tue, 5 Jan 2016 10:22:30 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jan Kara <jack@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dave Chinner <david@...morbit.com>,
	Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	X86 ML <x86@...nel.org>, XFS Developers <xfs@....sgi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v6 4/7] dax: add support for fsync/msync

On Tue, Jan 5, 2016 at 10:14 AM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> On Tue, Jan 05, 2016 at 09:20:47AM -0800, Dan Williams wrote:
[..]
>> My concern is whether flushing potentially invalid virtual addresses
>> is problematic on some architectures.  Maybe it's just FUD, but it's
>> less work in my opinion to just revalidate the address versus auditing
>> each arch for this concern.
>
> I don't think that the addresses have the potential of being invalid from the
> driver's point of view - we are still holding a reference on the block queue
> via dax_map_atomic(), so we should be protected against races vs block device
> removal.  I think the only question is whether it is okay to flush an address
> that we know to be valid from the block device's point of view, but which the
> filesystem may have truncated from being allocated to our inode.
>
> Does that all make sense?

Yes, I was confusing which revalidation we were talking about.  As
long as the dax_map_atomic() is there I don't think we need any
further revalidation.
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