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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     Vishal Verma <vishal.l.verma@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org,
        Huang Ying <ying.huang@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jonathan Cameron <Jonathan.Cameron@Huawei.com>,
        Jeff Moyer <jmoyer@redhat.com>,
        Vishal Verma <vishal.l.verma@intel.com>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory
 requests across memblocks
In-Reply-To: <20230720-vv-kmem_memmap-v2-2-88bdaab34993@intel.com>
References: <20230720-vv-kmem_memmap-v2-0-88bdaab34993@intel.com>
 <20230720-vv-kmem_memmap-v2-2-88bdaab34993@intel.com>
Date:   Sun, 23 Jul 2023 20:23:19 +0530
Message-ID: <87a5vmadcw.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Vishal Verma <vishal.l.verma@intel.com> writes:

> The MHP_MEMMAP_ON_MEMORY flag for hotplugged memory is currently
> restricted to 'memblock_size' chunks of memory being added. Adding a
> larger span of memory precludes memmap_on_memory semantics.
>
> For users of hotplug such as kmem, large amounts of memory might get
> added from the CXL subsystem. In some cases, this amount may exceed the
> available 'main memory' to store the memmap for the memory being added.
> In this case, it is useful to have a way to place the memmap on the
> memory being added, even if it means splitting the addition into
> memblock-sized chunks.
>
> Change add_memory_resource() to loop over memblock-sized chunks of
> memory if caller requested memmap_on_memory, and if other conditions for
> it are met,. Teach try_remove_memory() to also expect that a memory
> range being removed might have been split up into memblock sized chunks,
> and to loop through those as needed.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.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>
> ---
>  mm/memory_hotplug.c | 154 +++++++++++++++++++++++++++++++---------------------
>  1 file changed, 91 insertions(+), 63 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e9bcacbcbae2..20456f0d28e6 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1286,6 +1286,35 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
>  }
>  EXPORT_SYMBOL_GPL(mhp_supports_memmap_on_memory);
>  
> +static int add_memory_create_devices(int nid, struct memory_group *group,
> +				     u64 start, u64 size, mhp_t mhp_flags)
> +{
> +	struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> +	struct vmem_altmap mhp_altmap = {};
> +	int ret;
> +
> +	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
> +		mhp_altmap.free = PHYS_PFN(size);
> +		mhp_altmap.base_pfn = PHYS_PFN(start);
> +		params.altmap = &mhp_altmap;
> +	}
> +
> +	/* call arch's memory hotadd */
> +	ret = arch_add_memory(nid, start, size, &params);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* create memory block devices after memory was added */
> +	ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
> +					  group);
> +	if (ret) {
> +		arch_remove_memory(start, size, NULL);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
>   * and online/offline operations (triggered e.g. by sysfs).
> @@ -1294,11 +1323,10 @@ EXPORT_SYMBOL_GPL(mhp_supports_memmap_on_memory);
>   */
>  int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>  {
> -	struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> +	unsigned long memblock_size = memory_block_size_bytes();
>  	enum memblock_flags memblock_flags = MEMBLOCK_NONE;
> -	struct vmem_altmap mhp_altmap = {};
>  	struct memory_group *group = NULL;
> -	u64 start, size;
> +	u64 start, size, cur_start;
>  	bool new_node = false;
>  	int ret;
>  
> @@ -1339,27 +1367,20 @@ 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) {
> -		if (!mhp_supports_memmap_on_memory(size)) {
> -			ret = -EINVAL;
> +	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> +	    mhp_supports_memmap_on_memory(memblock_size)) {
> +		for (cur_start = start; cur_start < start + size;
> +		     cur_start += memblock_size) {
> +			ret = add_memory_create_devices(nid, group, cur_start,
> +							memblock_size,
> +							mhp_flags);
> +			if (ret)
> +				goto error;
> +		}

We should handle the below error details here. 

1) If we hit an error after some blocks got added, should we iterate over rest of the dev_dax->nr_range.
2) With some blocks added if we return a failure here, we remove the
resource in dax_kmem. Is that ok? 

IMHO error handling with partial creation of memory blocks in a resource range should be
documented with this change.


> +	} else {
> +		ret = add_memory_create_devices(nid, group, start, size, mhp_flags);
> +		if (ret)
>  			goto error;
> -		}
> -		mhp_altmap.free = PHYS_PFN(size);
> -		mhp_altmap.base_pfn = PHYS_PFN(start);
> -		params.altmap = &mhp_altmap;
> -	}
> -
> -	/* call arch's memory hotadd */
> -	ret = arch_add_memory(nid, start, size, &params);
> -	if (ret < 0)
> -		goto error;
> -
> -	/* create memory block devices after memory was added */
> -	ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
> -					  group);
> -	if (ret) {
> -		arch_remove_memory(start, size, NULL);
> -		goto error;
>  	}
>  
>  	if (new_node) {
> @@ -2035,12 +2056,38 @@ void try_offline_node(int nid)
>  }
>  EXPORT_SYMBOL(try_offline_node);
>  
> -static int __ref try_remove_memory(u64 start, u64 size)
> +static void __ref __try_remove_memory(int nid, u64 start, u64 size,
> +				     struct vmem_altmap *altmap)
>  {
> -	struct vmem_altmap mhp_altmap = {};
> -	struct vmem_altmap *altmap = NULL;
> -	unsigned long nr_vmemmap_pages;
> -	int rc = 0, nid = NUMA_NO_NODE;
> +	/* remove memmap entry */
> +	firmware_map_remove(start, start + size, "System RAM");
> +
> +	/*
> +	 * Memory block device removal under the device_hotplug_lock is
> +	 * a barrier against racing online attempts.
> +	 */
> +	remove_memory_block_devices(start, size);
> +
> +	mem_hotplug_begin();
> +
> +	arch_remove_memory(start, size, altmap);
> +
> +	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> +		memblock_phys_free(start, size);
> +		memblock_remove(start, size);
> +	}
> +
> +	release_mem_region_adjustable(start, size);
> +
> +	if (nid != NUMA_NO_NODE)
> +		try_offline_node(nid);
> +
> +	mem_hotplug_done();
> +}
> +
> +static int try_remove_memory(u64 start, u64 size)
> +{
> +	int rc, nid = NUMA_NO_NODE;
>  
>  	BUG_ON(check_hotplug_memory_range(start, size));
>  
> @@ -2058,20 +2105,21 @@ static int __ref try_remove_memory(u64 start, u64 size)
>  		return rc;
>  
>  	/*
> -	 * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
> -	 * the same granularity it was added - a single memory block.
> +	 * For memmap_on_memory, the altmaps could have been added on
> +	 * a per-memblock basis. Loop through the entire range if so,
> +	 * and remove each memblock and its altmap
>  	 */
>  	if (mhp_memmap_on_memory()) {
> -		nr_vmemmap_pages = walk_memory_blocks(start, size, NULL,
> -						      get_nr_vmemmap_pages_cb);
> -		if (nr_vmemmap_pages) {
> -			if (size != memory_block_size_bytes()) {
> -				pr_warn("Refuse to remove %#llx - %#llx,"
> -					"wrong granularity\n",
> -					start, start + size);
> -				return -EINVAL;
> -			}
> +		unsigned long memblock_size = memory_block_size_bytes();
> +		struct vmem_altmap mhp_altmap = {};
> +		struct vmem_altmap *altmap;
> +		u64 cur_start;
>  
> +		for (cur_start = start; cur_start < start + size;
> +		     cur_start += memblock_size) {
> +			unsigned long nr_vmemmap_pages =
> +				walk_memory_blocks(start, memblock_size, NULL,
> +						   get_nr_vmemmap_pages_cb);
>  			/*
>  			 * Let remove_pmd_table->free_hugepage_table do the
>  			 * right thing if we used vmem_altmap when hot-adding
> @@ -2079,33 +2127,13 @@ static int __ref try_remove_memory(u64 start, u64 size)
>  			 */
>  			mhp_altmap.alloc = nr_vmemmap_pages;
>  			altmap = &mhp_altmap;
> +			__try_remove_memory(nid, cur_start, memblock_size,
> +						 altmap);
>  		}
> +	} else {
> +		__try_remove_memory(nid, start, size, NULL);
>  	}
>  
> -	/* remove memmap entry */
> -	firmware_map_remove(start, start + size, "System RAM");
> -
> -	/*
> -	 * Memory block device removal under the device_hotplug_lock is
> -	 * a barrier against racing online attempts.
> -	 */
> -	remove_memory_block_devices(start, size);
> -
> -	mem_hotplug_begin();
> -
> -	arch_remove_memory(start, size, altmap);
> -
> -	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> -		memblock_phys_free(start, size);
> -		memblock_remove(start, size);
> -	}
> -
> -	release_mem_region_adjustable(start, size);
> -
> -	if (nid != NUMA_NO_NODE)
> -		try_offline_node(nid);
> -
> -	mem_hotplug_done();
>  	return 0;
>  }
>  
>
> -- 
> 2.41.0