Message-ID: <8b60e40a-1e8a-1f7c-a31d-ad2e511decd5@redhat.com>
Date:   Fri, 26 Jul 2019 10:34:47 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc:     dan.j.williams@...el.com, pasha.tatashin@...een.com,
        mhocko@...e.com, anshuman.khandual@....com,
        Jonathan.Cameron@...wei.com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] mm,memory_hotplug: Introduce MHP_MEMMAP_ON_MEMORY

On 25.07.19 18:02, Oscar Salvador wrote:
> This patch introduces MHP_MEMMAP_ON_MEMORY flag,
> and prepares the callers that add memory to take a "flags" parameter.
> This "flags" parameter will be evaluated later on in Patch#3
> to init mhp_restrictions struct.
> 
> The callers are:
> 
> add_memory
> __add_memory
> add_memory_resource
> 
> Unfortunately, we do not have a single entry point to add memory, as depending
> on the requisites of the caller, they want to hook up in different places,
> (e.g: Xen reserve_additional_memory()), so we have to spread the parameter
> in the three callers.
> 
> MHP_MEMMAP_ON_MEMORY flag parameter will specify to allocate memmaps
> from the hot-added range.
> If callers wants memmaps to be allocated per memory block, it will
> have to call add_memory() variants in memory-block granularity
> spanning the whole range, while if it wants to allocate memmaps
> per whole memory range, just one call will do.
> 
> Want to add 384MB (3 sections, 3 memory-blocks)
> e.g:
> 
> 	add_memory(0x1000, size_memory_block);
> 	add_memory(0x2000, size_memory_block);
> 	add_memory(0x3000, size_memory_block);
> 
> 	[memblock#0  ]
> 	[0 - 511 pfns      ] - vmemmaps for section#0
> 	[512 - 32767 pfns  ] - normal memory
> 
> 	[memblock#1 ]
> 	[32768 - 33279 pfns] - vmemmaps for section#1
> 	[33280 - 65535 pfns] - normal memory
> 
> 	[memblock#2 ]
> 	[65536 - 66047 pfns] - vmemmap for section#2
> 	[66048 - 98304 pfns] - normal memory

I wouldn't even care about documenting this right now. We have no user
so far, so spending 50% of the description on this topic isn't really
needed IMHO :)

> 
> or
> 	add_memory(0x1000, size_memory_block * 3);
> 
> 	[memblock #0 ]
>         [0 - 1533 pfns    ] - vmemmap for section#{0-2}
>         [1534 - 98304 pfns] - normal memory
> 
> When using larger memory blocks (1GB or 2GB), the principle is the same.
> 
> Of course, per whole-range granularity is nicer when it comes to have a large
> contigous area, while per memory-block granularity allows us to have flexibility
> when removing the memory.

E.g., in my virtio-mem I am currently adding all memory blocks
separately either way (to guranatee that remove_memory() works cleanly -
see __release_memory_resource()), and to control the amount of
not-offlined memory blocks (e.g., to make user space is actually
onlining them). As it's just a prototype, this might change of course in
the future.

> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  drivers/acpi/acpi_memhotplug.c |  2 +-
>  drivers/base/memory.c          |  2 +-
>  drivers/dax/kmem.c             |  2 +-
>  drivers/hv/hv_balloon.c        |  2 +-
>  drivers/s390/char/sclp_cmd.c   |  2 +-
>  drivers/xen/balloon.c          |  2 +-
>  include/linux/memory_hotplug.h | 25 ++++++++++++++++++++++---
>  mm/memory_hotplug.c            | 10 +++++-----
>  8 files changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index e294f44a7850..d91b3584d4b2 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -207,7 +207,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
>  		if (node < 0)
>  			node = memory_add_physaddr_to_nid(info->start_addr);
>  
> -		result = __add_memory(node, info->start_addr, info->length);
> +		result = __add_memory(node, info->start_addr, info->length, 0);
>  
>  		/*
>  		 * If the memory block has been used by the kernel, add_memory()
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 154d5d4a0779..d30d0f6c8ad0 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -521,7 +521,7 @@ static ssize_t probe_store(struct device *dev, struct device_attribute *attr,
>  
>  	nid = memory_add_physaddr_to_nid(phys_addr);
>  	ret = __add_memory(nid, phys_addr,
> -			   MIN_MEMORY_BLOCK_SIZE * sections_per_block);
> +			   MIN_MEMORY_BLOCK_SIZE * sections_per_block, 0);
>  
>  	if (ret)
>  		goto out;
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 3d0a7e702c94..e159184e0ba0 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -65,7 +65,7 @@ int dev_dax_kmem_probe(struct device *dev)
>  	new_res->flags = IORESOURCE_SYSTEM_RAM;
>  	new_res->name = dev_name(dev);
>  
> -	rc = add_memory(numa_node, new_res->start, resource_size(new_res));
> +	rc = add_memory(numa_node, new_res->start, resource_size(new_res), 0);
>  	if (rc) {
>  		release_resource(new_res);
>  		kfree(new_res);
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index 6fb4ea5f0304..beb92bc56186 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -731,7 +731,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
>  
>  		nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
>  		ret = add_memory(nid, PFN_PHYS((start_pfn)),
> -				(HA_CHUNK << PAGE_SHIFT));
> +				(HA_CHUNK << PAGE_SHIFT), 0);
>  
>  		if (ret) {
>  			pr_err("hot_add memory failed error is %d\n", ret);
> diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
> index 37d42de06079..f61026c7db7e 100644
> --- a/drivers/s390/char/sclp_cmd.c
> +++ b/drivers/s390/char/sclp_cmd.c
> @@ -406,7 +406,7 @@ static void __init add_memory_merged(u16 rn)
>  	if (!size)
>  		goto skip_add;
>  	for (addr = start; addr < start + size; addr += block_size)
> -		add_memory(numa_pfn_to_nid(PFN_DOWN(addr)), addr, block_size);
> +		add_memory(numa_pfn_to_nid(PFN_DOWN(addr)), addr, block_size, 0);
>  skip_add:
>  	first_rn = rn;
>  	num = 1;
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 4e11de6cde81..e4934ce40478 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -349,7 +349,7 @@ static enum bp_state reserve_additional_memory(void)
>  	mutex_unlock(&balloon_mutex);
>  	/* add_memory_resource() requires the device_hotplug lock */
>  	lock_device_hotplug();
> -	rc = add_memory_resource(nid, resource);
> +	rc = add_memory_resource(nid, resource, 0);
>  	unlock_device_hotplug();
>  	mutex_lock(&balloon_mutex);
>  
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index f46ea71b4ffd..45dece922d7c 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -54,6 +54,25 @@ enum {
>  };
>  
>  /*
> + * We want memmap (struct page array) to be allocated from the hotadded range.
> + * To do so, there are two possible ways depending on what the caller wants.
> + * 1) Allocate memmap pages whole hot-added range.
> + *    Here the caller will only call any add_memory() variant with the whole
> + *    memory address.
> + * 2) Allocate memmap pages per memblock
> + *    Here, the caller will call any add_memory() variant per memblock
> + *    granularity.
> + * The former implies that we will use the beginning of the hot-added range
> + * to store the memmap pages of the whole range, while the latter implies
> + * that we will use the beginning of each memblock to store its own memmap
> + * pages.

Can you make this documentation only state how MHP_MEMMAP_ON_MEMORY
works? (IOW, shrink it heavily to what we actually implement)

> + *
> + * Please note that this is only a hint, not a guarantee. Only selected
> + * architectures support it with SPARSE_VMEMMAP.
> + */
> +#define MHP_MEMMAP_ON_MEMORY	(1UL<<1)
> +
> +/*
>   * Restrictions for the memory hotplug:
>   * flags:  MHP_ flags
>   * altmap: alternative allocator for memmap array
> @@ -340,9 +359,9 @@ static inline void __remove_memory(int nid, u64 start, u64 size) {}
>  #endif /* CONFIG_MEMORY_HOTREMOVE */
>  
>  extern void __ref free_area_init_core_hotplug(int nid);
> -extern int __add_memory(int nid, u64 start, u64 size);
> -extern int add_memory(int nid, u64 start, u64 size);
> -extern int add_memory_resource(int nid, struct resource *resource);
> +extern int __add_memory(int nid, u64 start, u64 size, unsigned long flags);
> +extern int add_memory(int nid, u64 start, u64 size, unsigned long flags);
> +extern int add_memory_resource(int nid, struct resource *resource, unsigned long flags);
>  extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
>  		unsigned long nr_pages, struct vmem_altmap *altmap);
>  extern bool is_memblock_offlined(struct memory_block *mem);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9a82e12bd0e7..3d97c3711333 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1046,7 +1046,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
>   *
>   * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
>   */
> -int __ref add_memory_resource(int nid, struct resource *res)
> +int __ref add_memory_resource(int nid, struct resource *res, unsigned long flags)
>  {
>  	struct mhp_restrictions restrictions = {};
>  	u64 start, size;
> @@ -1123,7 +1123,7 @@ int __ref add_memory_resource(int nid, struct resource *res)
>  }
>  
>  /* requires device_hotplug_lock, see add_memory_resource() */
> -int __ref __add_memory(int nid, u64 start, u64 size)
> +int __ref __add_memory(int nid, u64 start, u64 size, unsigned long flags)
>  {
>  	struct resource *res;
>  	int ret;
> @@ -1132,18 +1132,18 @@ int __ref __add_memory(int nid, u64 start, u64 size)
>  	if (IS_ERR(res))
>  		return PTR_ERR(res);
>  
> -	ret = add_memory_resource(nid, res);
> +	ret = add_memory_resource(nid, res, flags);
>  	if (ret < 0)
>  		release_memory_resource(res);
>  	return ret;
>  }
>  
> -int add_memory(int nid, u64 start, u64 size)
> +int add_memory(int nid, u64 start, u64 size, unsigned long flags)
>  {
>  	int rc;
>  
>  	lock_device_hotplug();
> -	rc = __add_memory(nid, start, size);
> +	rc = __add_memory(nid, start, size, flags);
>  	unlock_device_hotplug();
>  
>  	return rc;
> 

Apart from the requested description/documentation changes

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David / dhildenb

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