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

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Message-ID: <x498tpznpax.fsf@segfault.boston.devel.redhat.com>
Date:   Wed, 25 Jan 2017 10:15:50 -0500
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Toshi Kani <toshi.kani@....com>, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, linux-nvdimm@...1.01.org,
        david@...morbit.com, linux-kernel@...r.kernel.org,
        Joe Perches <joe@...ches.com>, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5] DAX: enable iostat for read/write

Christoph Hellwig <hch@...radead.org> writes:

> On Thu, Jan 12, 2017 at 11:38:48AM -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.
>> 
>> 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.
>
> NAK.  DAX I/O should not be accounted for block device statistics.

Agreed, this is a layering violation.

Cheers,
Jeff