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Date:   Thu, 18 Jul 2019 09:26:09 +0300
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Leonardo Bras <leonardo@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Pasha Tatashin <Pavel.Tatashin@microsoft.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in
 ZONE_MOVABLE
References: <20190718024133.3873-1-leonardo@linux.ibm.com>
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On Wed, Jul 17, 2019 at 11:41:34PM -0300, Leonardo Bras wrote:
> Adds an option on kernel config to make hot-added memory online in
> ZONE_MOVABLE by default.
> 
> This would be great in systems with MEMORY_HOTPLUG_DEFAULT_ONLINE=y by
> allowing to choose which zone it will be auto-onlined
 
Please add more elaborate description of the problem you are solving and
the solution outline.


> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
>  drivers/base/memory.c |  3 +++
>  mm/Kconfig            | 14 ++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index f180427e48f4..378b585785c1 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -670,6 +670,9 @@ static int init_memory_block(struct memory_block **memory,
>  	mem->state = state;
>  	start_pfn = section_nr_to_pfn(mem->start_section_nr);
>  	mem->phys_device = arch_get_memory_phys_device(start_pfn);
> +#ifdef CONFIG_MEMORY_HOTPLUG_MOVABLE
> +	mem->online_type = MMOP_ONLINE_MOVABLE;
> +#endif

Does it has to be a compile time option?
Seems like this can be changed at run time or at least at boot.
  
>  	ret = register_memory(mem);
>  
> diff --git a/mm/Kconfig b/mm/Kconfig
> index f0c76ba47695..74e793720f43 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -180,6 +180,20 @@ config MEMORY_HOTREMOVE
>  	depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
>  	depends on MIGRATION
>  
> +config MEMORY_HOTPLUG_MOVABLE
> +	bool "Enhance the likelihood of hot-remove"
> +	depends on MEMORY_HOTREMOVE
> +	help
> +	  This option sets the hot-added memory zone to MOVABLE which
> +	  drastically reduces the chance of a hot-remove to fail due to
> +	  unmovable memory segments. Kernel memory can't be allocated in
> +	  this zone.
> +
> +	  Say Y here if you want to have better chance to hot-remove memory
> +	  that have been previously hot-added.
> +	  Say N here if you want to make all hot-added memory available to
> +	  kernel space.
> +
>  # Heavily threaded applications may benefit from splitting the mm-wide
>  # page_table_lock, so that faults on different parts of the user address
>  # space can be handled with less contention: split it at this NR_CPUS.
> -- 
> 2.20.1
> 

-- 
Sincerely yours,
Mike.