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Date: Thu, 7 May 2015 09:03:27 -0700
Message-ID: <CAPcyv4i5957h0PW5JL0rv4iurL=c7ppEFj3cDrrrMc4MQmJQGQ@mail.gmail.com>
Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer,
 introduce __pfn_t
From: Dan Williams <dan.j.williams@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Boaz Harrosh <boaz@plexistor.com>, Jan Kara <jack@suse.cz>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
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On Thu, May 7, 2015 at 8:58 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, May 7, 2015 at 8:40 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>>
>> blkdev_get(FMODE_EXCL) is the protection in this case.
>
> Ugh. That looks like a horrible nasty big hammer that will bite us
> badly some day. Since you'd have to hold it for the whole IO. But I
> guess it at least works.

Oh no, that wouldn't be per-I/O that would be permanent at
configuration set up time just like a raid member device.

Something like:
mdadm --create /dev/md0 --cache=/dev/pmem0p1 --storage=/dev/sda

> Anyway, I did want to say that while I may not be convinced about the
> approach, I think the patches themselves don't look horrible. I
> actually like your "__pfn_t". So while I (very obviously) have some
> doubts about this approach, it may be that the most convincing
> argument is just in the code.

Ok, I'll keep thinking about this and come back when we have a better
story about passing mmap'd persistent memory around in userspace.
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