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From:   Pavel Tatashin <pasha.tatashin@soleen.com>
Date:   Thu, 18 Jul 2019 08:19:46 -0400
Message-ID: <CA+CK2bBu7DnG73SaBDwf9cBceNvKnZDEqA-gBJmKC9K_rqgO+A@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE_MOVABLE
To:     Leonardo Bras <leonardo@linux.ibm.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Pasha Tatashin <Pavel.Tatashin@microsoft.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
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On Wed, Jul 17, 2019 at 10:42 PM Leonardo Bras <leonardo@linux.ibm.com> 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

This is a desired feature. From reading the code it looks to me that
auto-selection of online method type should be done in
memory_subsys_online().

When it is called from device online, mem->online_type should be -1:

if (mem->online_type < 0)
     mem->online_type = MMOP_ONLINE_KEEP;

Change it to:
if (mem->online_type < 0)
     mem->online_type = MMOP_DEFAULT_ONLINE_TYPE;

And in "linux/memory_hotplug.h"
#ifdef CONFIG_MEMORY_HOTPLUG_MOVABLE
#define MMOP_DEFAULT_ONLINE_TYPE MMOP_ONLINE_MOVABLE
#else
#define MMOP_DEFAULT_ONLINE_TYPE MMOP_ONLINE_KEEP
#endif

Could be expanded to support MMOP_ONLINE_KERNEL as well.

Pasha

>
> 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
>
>         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
>

On Wed, Jul 17, 2019 at 10:42 PM Leonardo Bras <leonardo@linux.ibm.com> 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
>
> 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
>
>         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
>