Date:	Mon, 14 Apr 2014 17:13:20 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
CC:	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	<gregkh@...uxfoundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [RFC PATCH v2] memory-hotplug: Update documentation to hide information
 about SECTIONS and remove end_phys_index

On 04/14/2014 04:43 PM, Li Zhong wrote:
> Seems we all agree that information about SECTION, e.g. section size,
> sections per memory block should be kept as kernel internals, and not
> exposed to userspace.
> 
> This patch updates Documentation/memory-hotplug.txt to refer to memory
> blocks instead of memory sections where appropriate and added a
> paragraph to explain that memory blocks are made of memory sections.
> The documentation update is mostly provided by Nathan.
> 
> Also, as end_phys_index in code is actually not the end section id, but
> the end memory block id, which should always be the same as phys_index.
> So it is removed here.
> 
> Signed-off-by: Li Zhong <zhong@...ux.vnet.ibm.com>

Reviewed-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>

Still the nitpick there.

> ---
>  Documentation/memory-hotplug.txt |  125 +++++++++++++++++++-------------------
>  drivers/base/memory.c            |   12 ----
>  2 files changed, 61 insertions(+), 76 deletions(-)
> 
> diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
> index 58340d5..1aa239f 100644
> --- a/Documentation/memory-hotplug.txt
> +++ b/Documentation/memory-hotplug.txt
> @@ -88,16 +88,21 @@ phase by hand.
>  
>  1.3. Unit of Memory online/offline operation
>  ------------
> -Memory hotplug uses SPARSEMEM memory model. SPARSEMEM divides the whole memory
> -into chunks of the same size. The chunk is called a "section". The size of
> -a section is architecture dependent. For example, power uses 16MiB, ia64 uses
> -1GiB. The unit of online/offline operation is "one section". (see Section 3.)
> +Memory hotplug uses SPARSEMEM memory model which allows memory to be divided
> +into chunks of the same size. These chunks are called "sections". The size of
> +a memory section is architecture dependent. For example, power uses 16MiB, ia64
> +uses 1GiB.
>  
> -To determine the size of sections, please read this file:
> +Memory sections are combined into chunks referred to as "memory blocks". The
> +size of a memory block is architecture dependent and represents the logical
> +unit upon which memory online/offline operations are to be performed. The
> +default size of a memory block is the same as memory section size unless an
> +architecture specifies otherwise. (see Section 3.)
> +
> +To determine the size (in bytes) of a memory block please read this file:
>  
>  /sys/devices/system/memory/block_size_bytes
>  
> -This file shows the size of sections in byte.
>  
>  -----------------------
>  2. Kernel Configuration
> @@ -123,42 +128,35 @@ config options.
>      (CONFIG_ACPI_CONTAINER).
>      This option can be kernel module too.
>  
> +
>  --------------------------------
> -4 sysfs files for memory hotplug
> +3 sysfs files for memory hotplug
>  --------------------------------
> -All sections have their device information in sysfs.  Each section is part of
> -a memory block under /sys/devices/system/memory as
> +All memory blocks have their device information in sysfs.  Each memory block
> +is described under /sys/devices/system/memory as
>  
>  /sys/devices/system/memory/memoryXXX
> -(XXX is the section id.)
> +(XXX is the memory block id.)
>  
> -Now, XXX is defined as (start_address_of_section / section_size) of the first
> -section contained in the memory block.  The files 'phys_index' and
> -'end_phys_index' under each directory report the beginning and end section id's
> -for the memory block covered by the sysfs directory.  It is expected that all
> +For the memory block covered by the sysfs directory.  It is expected that all
>  memory sections in this range are present and no memory holes exist in the
>  range. Currently there is no way to determine if there is a memory hole, but
>  the existence of one should not affect the hotplug capabilities of the memory
>  block.
>  
> -For example, assume 1GiB section size. A device for a memory starting at
> +For example, assume 1GiB memory block size. A device for a memory starting at
>  0x100000000 is /sys/device/system/memory/memory4
>  (0x100000000 / 1Gib = 4)
>  This device covers address range [0x100000000 ... 0x140000000)
>  
> -Under each section, you can see 4 or 5 files, the end_phys_index file being
> -a recent addition and not present on older kernels.
> +Under each memory block, you can see 4 files:
>  
> -/sys/devices/system/memory/memoryXXX/start_phys_index
> -/sys/devices/system/memory/memoryXXX/end_phys_index
> +/sys/devices/system/memory/memoryXXX/phys_index
>  /sys/devices/system/memory/memoryXXX/phys_device
>  /sys/devices/system/memory/memoryXXX/state
>  /sys/devices/system/memory/memoryXXX/removable
>  
> -'phys_index'      : read-only and contains section id of the first section
> -		    in the memory block, same as XXX.
> -'end_phys_index'  : read-only and contains section id of the last section
> -		    in the memory block.
> +'phys_index'      : read-only and contains memory block id, same as XXX.
>  'state'           : read-write
>                      at read:  contains online/offline state of memory.
>                      at write: user can specify "online_kernel",
> @@ -185,6 +183,7 @@ For example:
>  A backlink will also be created:
>  /sys/devices/system/memory/memory9/node0 -> ../../node/node0
>  
> +
>  --------------------------------
>  4. Physical memory hot-add phase
>  --------------------------------
> @@ -227,11 +226,10 @@ You can tell the physical address of new memory to the kernel by
>  
>  % echo start_address_of_new_memory > /sys/devices/system/memory/probe
>  
> -Then, [start_address_of_new_memory, start_address_of_new_memory + section_size)
> -memory range is hot-added. In this case, hotplug script is not called (in
> -current implementation). You'll have to online memory by yourself.
> -Please see "How to online memory" in this text.
> -
> +Then, [start_address_of_new_memory, start_address_of_new_memory +
> +memory_block_size] memory range is hot-added. In this case, hotplug script is
> +not called (in current implementation). You'll have to online memory by
> +yourself.  Please see "How to online memory" in this text.
>  
>  
>  ------------------------------
> @@ -240,36 +238,36 @@ Please see "How to online memory" in this text.
>  
>  5.1. State of memory
>  ------------
> -To see (online/offline) state of memory section, read 'state' file.
> +To see (online/offline) state of a memory block, read 'state' file.
>  
>  % cat /sys/device/system/memory/memoryXXX/state
>  
>  
> -If the memory section is online, you'll read "online".
> -If the memory section is offline, you'll read "offline".
> +If the memory block is online, you'll read "online".
> +If the memory block is offline, you'll read "offline".
>  
>  
>  5.2. How to online memory
>  ------------
>  Even if the memory is hot-added, it is not at ready-to-use state.
> -For using newly added memory, you have to "online" the memory section.
> +For using newly added memory, you have to "online" the memory block.
>  
> -For onlining, you have to write "online" to the section's state file as:
> +For onlining, you have to write "online" to the memory block's state file as:
>  
>  % echo online > /sys/devices/system/memory/memoryXXX/state
>  
> -This onlining will not change the ZONE type of the target memory section,
> -If the memory section is in ZONE_NORMAL, you can change it to ZONE_MOVABLE:
> +This onlining will not change the ZONE type of the target memory block,
> +If the memory block is in ZONE_NORMAL, you can change it to ZONE_MOVABLE:
>  
>  % echo online_movable > /sys/devices/system/memory/memoryXXX/state
> -(NOTE: current limit: this memory section must be adjacent to ZONE_MOVABLE)
> +(NOTE: current limit: this memory block must be adjacent to ZONE_MOVABLE)
>  
> -And if the memory section is in ZONE_MOVABLE, you can change it to ZONE_NORMAL:
> +And if the memory block is in ZONE_MOVABLE, you can change it to ZONE_NORMAL:
>  
>  % echo online_kernel > /sys/devices/system/memory/memoryXXX/state
> -(NOTE: current limit: this memory section must be adjacent to ZONE_NORMAL)
> +(NOTE: current limit: this memory block must be adjacent to ZONE_NORMAL)
>  
> -After this, section memoryXXX's state will be 'online' and the amount of
> +After this, memory block XXX's state will be 'online' and the amount of
>  available memory will be increased.
>  
>  Currently, newly added memory is added as ZONE_NORMAL (for powerpc, ZONE_DMA).
> @@ -284,22 +282,22 @@ This may be changed in future.
>  6.1 Memory offline and ZONE_MOVABLE
>  ------------
>  Memory offlining is more complicated than memory online. Because memory offline
> -has to make the whole memory section be unused, memory offline can fail if
> -the section includes memory which cannot be freed.
> +has to make the whole memory block be unused, memory offline can fail if
> +the memort block includes memory which cannot be freed.
       ^^^^^^


>  
>  In general, memory offline can use 2 techniques.
>  
> -(1) reclaim and free all memory in the section.
> -(2) migrate all pages in the section.
> +(1) reclaim and free all memory in the memory block.
> +(2) migrate all pages in the memory block.
>  
>  In the current implementation, Linux's memory offline uses method (2), freeing
> -all  pages in the section by page migration. But not all pages are
> +all  pages in the memory block by page migration. But not all pages are
>  migratable. Under current Linux, migratable pages are anonymous pages and
> -page caches. For offlining a section by migration, the kernel has to guarantee
> -that the section contains only migratable pages.
> +page caches. For offlining a memory block by migration, the kernel has to
> +guarantee that the memory block contains only migratable pages.
>  
> -Now, a boot option for making a section which consists of migratable pages is
> -supported. By specifying "kernelcore=" or "movablecore=" boot option, you can
> +Now, a boot option for making a memory block which consists of migratable pages
> +is supported. By specifying "kernelcore=" or "movablecore=" boot option, you can
>  create ZONE_MOVABLE...a zone which is just used for movable pages.
>  (See also Documentation/kernel-parameters.txt)
>  
> @@ -315,28 +313,27 @@ creates ZONE_MOVABLE as following.
>    Size of memory for movable pages (for offline) is ZZZZ.
>  
>  
> -Note) Unfortunately, there is no information to show which section belongs
> +Note: Unfortunately, there is no information to show which memory block belongs
>  to ZONE_MOVABLE. This is TBD.
>  
>  
>  6.2. How to offline memory
>  ------------
> -You can offline a section by using the same sysfs interface that was used in
> -memory onlining.
> +You can offline a memory block by using the same sysfs interface that was used
> +in memory onlining.
>  
>  % echo offline > /sys/devices/system/memory/memoryXXX/state
>  
> -If offline succeeds, the state of the memory section is changed to be "offline".
> +If offline succeeds, the state of the memory block is changed to be "offline".
>  If it fails, some error core (like -EBUSY) will be returned by the kernel.
> -Even if a section does not belong to ZONE_MOVABLE, you can try to offline it.
> -If it doesn't contain 'unmovable' memory, you'll get success.
> +Even if a memory block does not belong to ZONE_MOVABLE, you can try to offline
> +it.  If it doesn't contain 'unmovable' memory, you'll get success.
>  
> -A section under ZONE_MOVABLE is considered to be able to be offlined easily.
> -But under some busy state, it may return -EBUSY. Even if a memory section
> -cannot be offlined due to -EBUSY, you can retry offlining it and may be able to
> -offline it (or not).
> -(For example, a page is referred to by some kernel internal call and released
> - soon.)
> +A memory block under ZONE_MOVABLE is considered to be able to be offlined
> +easily.  But under some busy state, it may return -EBUSY. Even if a memory
> +block cannot be offlined due to -EBUSY, you can retry offlining it and may be
> +able to offline it (or not). (For example, a page is referred to by some kernel
> +internal call and released soon.)
>  
>  Consideration:
>  Memory hotplug's design direction is to make the possibility of memory offlining
> @@ -373,11 +370,11 @@ MEMORY_GOING_OFFLINE
>    Generated to begin the process of offlining memory. Allocations are no
>    longer possible from the memory but some of the memory to be offlined
>    is still in use. The callback can be used to free memory known to a
> -  subsystem from the indicated memory section.
> +  subsystem from the indicated memory block.
>  
>  MEMORY_CANCEL_OFFLINE
>    Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from
> -  the section that we attempted to offline.
> +  the memory block that we attempted to offline.
>  
>  MEMORY_OFFLINE
>    Generated after offlining memory is complete.
> @@ -413,8 +410,8 @@ node if necessary.
>  --------------
>    - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
>      sysctl or new control file.
> -  - showing memory section and physical device relationship.
> -  - showing memory section is under ZONE_MOVABLE or not
> +  - showing memory block and physical device relationship.
> +  - showing memory block is under ZONE_MOVABLE or not
>    - test and make it better memory offlining.
>    - support HugeTLB page migration and offlining.
>    - memmap removing at memory offline.
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index bece691..89f752d 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -118,16 +118,6 @@ static ssize_t show_mem_start_phys_index(struct device *dev,
>  	return sprintf(buf, "%08lx\n", phys_index);
>  }
>  
> -static ssize_t show_mem_end_phys_index(struct device *dev,
> -			struct device_attribute *attr, char *buf)
> -{
> -	struct memory_block *mem = to_memory_block(dev);
> -	unsigned long phys_index;
> -
> -	phys_index = mem->end_section_nr / sections_per_block;
> -	return sprintf(buf, "%08lx\n", phys_index);
> -}
> -
>  /*
>   * Show whether the section of memory is likely to be hot-removable
>   */
> @@ -384,7 +374,6 @@ static ssize_t show_phys_device(struct device *dev,
>  }
>  
>  static DEVICE_ATTR(phys_index, 0444, show_mem_start_phys_index, NULL);
> -static DEVICE_ATTR(end_phys_index, 0444, show_mem_end_phys_index, NULL);
>  static DEVICE_ATTR(state, 0644, show_mem_state, store_mem_state);
>  static DEVICE_ATTR(phys_device, 0444, show_phys_device, NULL);
>  static DEVICE_ATTR(removable, 0444, show_mem_removable, NULL);
> @@ -529,7 +518,6 @@ struct memory_block *find_memory_block(struct mem_section *section)
>  
>  static struct attribute *memory_memblk_attrs[] = {
>  	&dev_attr_phys_index.attr,
> -	&dev_attr_end_phys_index.attr,
>  	&dev_attr_state.attr,
>  	&dev_attr_phys_device.attr,
>  	&dev_attr_removable.attr,
> 
> 
> 
> 
> .
> 


-- 
Thanks.
Zhang Yanfei
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