linux-kernel - Re: revamp vmem_altmap / dev

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Date:   Mon, 8 Jan 2018 13:27:13 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, linux-nvdimm@...ts.01.org,
        X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: revamp vmem_altmap / dev_pagemap handling V3

On Mon, Jan 8, 2018 at 12:25 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Mon 08-01-18 11:44:02, Dan Williams wrote:
>> On Mon, Jan 8, 2018 at 3:26 AM, Christoph Hellwig <hch@....de> wrote:
>> > Any chance to get this fully reviewed and picked up before the
>> > end of the merge window?
>>
>> I'm fine carrying these through the nvdimm tree, but I'd need an ack
>> from the mm folks for all the code touches related to arch_add_memory.
>
> I am sorry to be slow here but I am out of time right now - yeah having
> a lot of fun kaiser time. I didn't get to look at these patches at all
> yet but the changelog suggests that you want to remove vmem_altmap.
> I've had plans to (ab)use this for self hosted struct pages for memory
> hotplug http://lkml.kernel.org/r/20170801124111.28881-1-mhocko@kernel.org
> That work is stalled though because it is buggy and I was too busy to
> finish that work. Anyway, if you believe that removing vmem_altmap is a
> good step in general I will find another way. I wasn't really happy how
> the whole thing is grafted to the memory hotplug and (ab)used it only
> because it was handy and ready for reuse.

You misread, these are keeping vmem_altmap and cleaning up the usage
to pass the vmem_altmap pointer through all paths rather than the
tricky radix lookup we were doing previously.

> Anyway if you need a review of mm parts from me, you will have to wait
> some more. If this requires some priority then go ahead and merge
> it. Times are just too crazy right now.

Since you were planning on reusing vmem_altmap I think these patches
make your job easier. I don't see the risk in merging these, we've
squeezed out a few bugs and all the nvdimm unit tests are passing.

> Sorry about that.

No worries, quite a few of us are in that same boat.