linux-kernel - Re: [PATCH v2 8/8] mm/memory_hotplug: allow to specify a default online

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Date:   Tue, 17 Mar 2020 12:01:21 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, linux-hyperv@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v2 8/8] mm/memory_hotplug: allow to specify a default
 online_type

On Tue 17-03-20 11:49:42, David Hildenbrand wrote:
> For now, distributions implement advanced udev rules to essentially
> - Don't online any hotplugged memory (s390x)
> - Online all memory to ZONE_NORMAL (e.g., most virt environments like
>   hyperv)
> - Online all memory to ZONE_MOVABLE in case the zone imbalance is taken
>   care of (e.g., bare metal, special virt environments)
> 
> In summary: All memory is usually onlined the same way, however, the
> kernel always has to ask user space to come up with the same answer.
> E.g., Hyper-V always waits for a memory block to get onlined before
> continuing, otherwise it might end up adding memory faster than
> hotplugging it, which can result in strange OOM situations. This waiting
> slows down adding of a bigger amount of memory.
> 
> Let's allow to specify a default online_type, not just "online" and
> "offline". This allows distributions to configure the default online_type
> when booting up and be done with it.
> 
> We can now specify "offline", "online", "online_movable" and
> "online_kernel" via
> - "memhp_default_state=" on the kernel cmdline
> - /sys/devices/system/memory/auto_online_blocks
> just like we are able to specify for a single memory block via
> /sys/devices/system/memory/memoryX/state
> 
> Reviewed-by: Wei Yang <richard.weiyang@...il.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

As I've said earlier and several times already, I really dislike this
interface. But it is fact that this patch doesn't make it any worse.
Quite contrary, so feel free to add
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  drivers/base/memory.c          | 11 +++++------
>  include/linux/memory_hotplug.h |  2 ++
>  mm/memory_hotplug.c            |  8 ++++----
>  3 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 8d3e16dab69f..2b09b68b9f78 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -35,7 +35,7 @@ static const char *const online_type_to_str[] = {
>  	[MMOP_ONLINE_MOVABLE] = "online_movable",
>  };
>  
> -static int memhp_online_type_from_str(const char *str)
> +int memhp_online_type_from_str(const char *str)
>  {
>  	int i;
>  
> @@ -394,13 +394,12 @@ static ssize_t auto_online_blocks_store(struct device *dev,
>  					struct device_attribute *attr,
>  					const char *buf, size_t count)
>  {
> -	if (sysfs_streq(buf, "online"))
> -		memhp_default_online_type = MMOP_ONLINE;
> -	else if (sysfs_streq(buf, "offline"))
> -		memhp_default_online_type = MMOP_OFFLINE;
> -	else
> +	const int online_type = memhp_online_type_from_str(buf);
> +
> +	if (online_type < 0)
>  		return -EINVAL;
>  
> +	memhp_default_online_type = online_type;
>  	return count;
>  }
>  
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index c6e090b34c4b..ef55115320fb 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -117,6 +117,8 @@ extern int arch_add_memory(int nid, u64 start, u64 size,
>  			struct mhp_restrictions *restrictions);
>  extern u64 max_mem_size;
>  
> +extern int memhp_online_type_from_str(const char *str);
> +
>  /* Default online_type (MMOP_*) when new memory blocks are added. */
>  extern int memhp_default_online_type;
>  /* If movable_node boot option specified */
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1975a2b99a2b..9916977b6ee1 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -74,10 +74,10 @@ int memhp_default_online_type = MMOP_ONLINE;
>  
>  static int __init setup_memhp_default_state(char *str)
>  {
> -	if (!strcmp(str, "online"))
> -		memhp_default_online_type = MMOP_ONLINE;
> -	else if (!strcmp(str, "offline"))
> -		memhp_default_online_type = MMOP_OFFLINE;
> +	const int online_type = memhp_online_type_from_str(str);
> +
> +	if (online_type >= 0)
> +		memhp_default_online_type = online_type;
>  
>  	return 1;
>  }
> -- 
> 2.24.1

-- 
Michal Hocko
SUSE Labs