linux-kernel - Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE

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Date:   Thu, 18 Jul 2019 08:12:33 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Leonardo Bras <leonardo@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in
 ZONE_MOVABLE

On Wed, 2019-07-17 at 23:41 -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

We do already have "movable_node" boot option, which exactly has that
effect.
Any hotplugged range will be placed in ZONE_MOVABLE.

Why do we need yet another option to achieve the same? Was not that
enough for your case?

> 
> Signed-off-by: Leonardo Bras <leonardo@...ux.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
>  
>  	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.
-- 
Oscar Salvador
SUSE L3