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Message-ID: <cd7c5f6b-d668-4fab-8e7e-4f41018067c5@redhat.com>
Date:   Thu, 14 Dec 2023 10:10:43 +0100
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Subject: Re: [PATCH v5 3/4] mm/memory_hotplug: export
 mhp_supports_memmap_on_memory()
Content-Language: en-US
To:     Vishal Verma <vishal.l.verma@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>
Cc:     linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev,
        linux-cxl@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Huang Ying <ying.huang@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-mm@kvack.org, Michal Hocko <mhocko@suse.com>
References: <20231214-vv-dax_abi-v5-0-3f7b006960b4@intel.com>
 <20231214-vv-dax_abi-v5-3-3f7b006960b4@intel.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat
In-Reply-To: <20231214-vv-dax_abi-v5-3-3f7b006960b4@intel.com>
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Precedence: bulk

On 14.12.23 08:37, Vishal Verma wrote:
> In preparation for adding sysfs ABI to toggle memmap_on_memory semantics
> for drivers adding memory, export the mhp_supports_memmap_on_memory()
> helper. This allows drivers to check if memmap_on_memory support is
> available before trying to request it, and display an appropriate
> message if it isn't available. As part of this, remove the size argument
> to this - with recent updates to allow memmap_on_memory for larger
> ranges, and the internal splitting of altmaps into respective memory
> blocks, the size argument is meaningless.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>   include/linux/memory_hotplug.h |  6 ++++++
>   mm/memory_hotplug.c            | 17 ++++++-----------
>   2 files changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 7d2076583494..ebc9d528f00c 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -121,6 +121,7 @@ struct mhp_params {
>   
>   bool mhp_range_allowed(u64 start, u64 size, bool need_mapping);
>   struct range mhp_get_pluggable_range(bool need_mapping);
> +bool mhp_supports_memmap_on_memory(void);
>   
>   /*
>    * Zone resizing functions
> @@ -262,6 +263,11 @@ static inline bool movable_node_is_enabled(void)
>   	return false;
>   }
>   
> +static bool mhp_supports_memmap_on_memory(void)
> +{
> +	return false;
> +}
> +
>   static inline void pgdat_kswapd_lock(pg_data_t *pgdat) {}
>   static inline void pgdat_kswapd_unlock(pg_data_t *pgdat) {}
>   static inline void pgdat_kswapd_lock_init(pg_data_t *pgdat) {}
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 926e1cfb10e9..751664c519f7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1325,7 +1325,7 @@ static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size)
>   }
>   #endif
>   
> -static bool mhp_supports_memmap_on_memory(unsigned long size)
> +bool mhp_supports_memmap_on_memory(void)
>   {
>   	unsigned long vmemmap_size = memory_block_memmap_size();
>   	unsigned long memmap_pages = memory_block_memmap_on_memory_pages();
> @@ -1334,17 +1334,11 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
>   	 * Besides having arch support and the feature enabled at runtime, we
>   	 * need a few more assumptions to hold true:
>   	 *
> -	 * a) We span a single memory block: memory onlining/offlinin;g happens
> -	 *    in memory block granularity. We don't want the vmemmap of online
> -	 *    memory blocks to reside on offline memory blocks. In the future,
> -	 *    we might want to support variable-sized memory blocks to make the
> -	 *    feature more versatile.
> -	 *
> -	 * b) The vmemmap pages span complete PMDs: We don't want vmemmap code
> +	 * a) The vmemmap pages span complete PMDs: We don't want vmemmap code
>   	 *    to populate memory from the altmap for unrelated parts (i.e.,
>   	 *    other memory blocks)
>   	 *
> -	 * c) The vmemmap pages (and thereby the pages that will be exposed to
> +	 * b) The vmemmap pages (and thereby the pages that will be exposed to
>   	 *    the buddy) have to cover full pageblocks: memory onlining/offlining
>   	 *    code requires applicable ranges to be page-aligned, for example, to
>   	 *    set the migratetypes properly.
> @@ -1356,7 +1350,7 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
>   	 *       altmap as an alternative source of memory, and we do not exactly
>   	 *       populate a single PMD.
>   	 */
> -	if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
> +	if (!mhp_memmap_on_memory())
>   		return false;
>   
>   	/*
> @@ -1379,6 +1373,7 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
>   
>   	return arch_supports_memmap_on_memory(vmemmap_size);
>   }
> +EXPORT_SYMBOL_GPL(mhp_supports_memmap_on_memory);
>   
>   static void __ref remove_memory_blocks_and_altmaps(u64 start, u64 size)
>   {
> @@ -1512,7 +1507,7 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>   	 * Self hosted memmap array
>   	 */
>   	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> -	    mhp_supports_memmap_on_memory(memory_block_size_bytes())) {
> +	    mhp_supports_memmap_on_memory()) {
>   		ret = create_altmaps_and_memory_blocks(nid, group, start, size);
>   		if (ret)
>   			goto error;
> 

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb