linux-kernel - Re: [PATCH] mm/hotplug: Reorder memblock_[free|remove]() calls in try_remove

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Date:   Tue, 24 Sep 2019 20:13:35 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] mm/hotplug: Reorder memblock_[free|remove]() calls in
 try_remove_memory()

On Mon, 23 Sep 2019 11:16:38 +0530 Anshuman Khandual <anshuman.khandual@....com> wrote:

> 
> 
> On 09/16/2019 11:17 AM, Anshuman Khandual wrote:
> > In add_memory_resource() the memory range to be hot added first gets into
> > the memblock via memblock_add() before arch_add_memory() is called on it.
> > Reverse sequence should be followed during memory hot removal which already
> > is being followed in add_memory_resource() error path. This now ensures
> > required re-order between memblock_[free|remove]() and arch_remove_memory()
> > during memory hot-remove.
> > 
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Oscar Salvador <osalvador@...e.de>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: David Hildenbrand <david@...hat.com>
> > Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > ---
> > Original patch https://lkml.org/lkml/2019/9/3/327
> > 
> > Memory hot remove now works on arm64 without this because a recent commit
> > 60bb462fc7ad ("drivers/base/node.c: simplify unregister_memory_block_under_nodes()").
> > 
> > David mentioned that re-ordering should still make sense for consistency
> > purpose (removing stuff in the reverse order they were added). This patch
> > is now detached from arm64 hot-remove series.
> > 
> > https://lkml.org/lkml/2019/9/3/326
>
> ...
>
> Hello Andrew,
> 
> Any feedbacks on this, does it look okay ?
> 

Well.  I'd parked this for 5.4-rc1 processing because it looked like a
cleanup.

But waaaay down below the ^---$ line I see "Memory hot remove now works
on arm64".  Am I correct in believing that 60bb462fc7ad broke arm64 mem
hot remove?  And that this patch fixes a serious regression?  If so,
that should have been right there in the patch title and changelog!