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From:   Jeff Moyer <jmoyer@redhat.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Oscar Salvador <osalvador@suse.de>, Qian Cai <cai@lca.pw>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()
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Date:   Fri, 14 Jun 2019 13:08:48 -0400
In-Reply-To: <16108dac-a4ca-aa87-e3b0-a79aebdcfafd@linux.ibm.com> (Aneesh
        Kumar K. V.'s message of "Fri, 14 Jun 2019 22:25:18 +0530")
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"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> On 6/14/19 10:06 PM, Dan Williams wrote:
>> On Fri, Jun 14, 2019 at 9:26 AM Aneesh Kumar K.V
>> <aneesh.kumar@linux.ibm.com> wrote:
>
>>> Why not let the arch
>>> arch decide the SUBSECTION_SHIFT and default to one subsection per
>>> section if arch is not enabled to work with subsection.
>>
>> Because that keeps the implementation from ever reaching a point where
>> a namespace might be able to be moved from one arch to another. If we
>> can squash these arch differences then we can have a common tool to
>> initialize namespaces outside of the kernel. The one wrinkle is
>> device-dax that wants to enforce the mapping size,
>
> The fsdax have a much bigger issue right? The file system block size
> is the same as PAGE_SIZE and we can't make it portable across archs
> that support different PAGE_SIZE?

File system blocks are not tied to page size.  They can't be *bigger*
than the page size currently, but they can be smaller.

Still, I don't see that as an arugment against trying to make the
namespaces work across architectures.  Consider a user who only has
sector mode namespaces.  We'd like that to work if at all possible.

-Jeff