linux-kernel - Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap

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Date:   Tue, 30 Oct 2018 09:05:27 +0100
From:   Oscar Salvador <osalvador.vilardaga@...il.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-nvdimm@...ts.01.org,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        dave.hansen@...el.com, Jerome Glisse <jglisse@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>, mingo@...nel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        yi.z.zhang@...ux.intel.com
Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the
 point where we init pgmap

> Yes, the hotplug lock was part of the original issue. However that
> starts to drift into the area I believe Oscar was working on as a part
> of his patch set in encapsulating the move_pfn_range_to_zone and other
> calls that were contained in the hotplug lock into their own functions.

While reworking it for my patchset, I thought that we can move
move_pfn_range_to_zone
out of hotplug lock.
But then I __think__ we would have to move init_currently_empty_zone() within
the span lock as zone->zone_start_pfn is being touched there.
At least that is what the zone locking rules say about it.

Since I saw that Dan was still reworking his patchset about unify HMM/devm code,
I just took one step back and I went simpler [1].
The main reason for backing off was I felt a bit demotivated due to
the lack of feedback,
and I did not want to interfer either with your work or Dan's work.
Plus I also was unsure about some other things like whether it is ok calling
kasan_add_zero_shadow/kasan_remove_zero_shadow out of the lock.
So I decided to make less changes in regard of HMM/devm.

Unfortunately, I did not get a lot of feedback there yet.
Just some reviews from David and a confirmation that fixes one of the
issues Jonathan reported [2].

>
> I was hoping to wait until after Dan's HMM patches and Oscar's changes
> had been sorted before I get into any further refactor of this specific
> code.

I plan to ping the series, but I wanted to give more time to people
since we are in the merge window now.

[1] https://patchwork.kernel.org/cover/10642049/
[2] https://patchwork.kernel.org/patch/10642057/#22275173