linux-kernel - Re: [PATCH v5 2/7] mm, devm_memremap_pages: Kill mapping "System RAM" support

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Date:   Fri, 14 Sep 2018 10:40:52 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/7] mm, devm_memremap_pages: Kill mapping "System RAM" support

On Fri, Sep 14, 2018 at 6:14 AM, Christoph Hellwig <hch@....de> wrote:
> On Wed, Sep 12, 2018 at 07:22:11PM -0700, Dan Williams wrote:
>> Given the fact that devm_memremap_pages() requires a percpu_ref that is
>> torn down by devm_memremap_pages_release() the current support for
>> mapping RAM is broken.
>
> I agree.  Do you remember why we even added it in the first place?

It was initially a copy over from memremap() that catches these
attempts and returns a direct-map pointer.