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

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Message-Id: <20190916063612.GA1502@linux.ibm.com>
Date:   Mon, 16 Sep 2019 09:36:12 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.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, Sep 16, 2019 at 11:17:37AM +0530, 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
> 
>  mm/memory_hotplug.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c73f09913165..355c466e0621 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
> 
>  	/* remove memmap entry */
>  	firmware_map_remove(start, start + size, "System RAM");
> -	memblock_free(start, size);
> -	memblock_remove(start, size);
> 
>  	/* remove memory block devices before removing memory */
>  	remove_memory_block_devices(start, size);
> 
>  	arch_remove_memory(nid, start, size, NULL);
> +	memblock_free(start, size);

I don't see memblock_reserve() anywhere in memory_hotplug.c, so the
memblock_free() call here seems superfluous. I think it can be simply
dropped.

> +	memblock_remove(start, size);
>  	__release_memory_resource(start, size);
> 
>  	try_offline_node(nid);
> -- 
> 2.20.1
> 
> 

-- 
Sincerely yours,
Mike.