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Date: Fri, 11 Apr 2014 13:54:52 -0500 From: Nathan Fontenot <nfont@...ux.vnet.ibm.com> To: Li Zhong <zhong@...ux.vnet.ibm.com> CC: 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>, Zhang Yanfei <zhangyanfei@...fujitsu.com> Subject: Re: [RFC PATCH] memory driver: make phys_index/end_phys_index reflect the start/end section number On 04/09/2014 11:17 PM, Li Zhong wrote: > On Wed, 2014-04-09 at 12:39 -0500, Nathan Fontenot wrote: >> On 04/08/2014 02:47 PM, Dave Hansen wrote: >>> >>> That document really needs to be updated to stop referring to sections >>> (at least in the descriptions of the user interface). We can not change >>> the units of phys_index/end_phys_index without also changing >>> block_size_bytes. >>> >> >> Here is a first pass at updating the documentation. >> >> I have tried to update the documentation to refer to memory blocks instead >> of memory sections where appropriate and added a paragraph to explain >> that memory blocks are mode of memory sections. >> >> Thoughts? > > If we all agree to hide the information about sections, then I think we > also need to update the section id's used for phys_index/end_phys_index, > something like following on top of yours? > > -- > diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt > index 92d15e2..9fbb025 100644 > --- a/Documentation/memory-hotplug.txt > +++ b/Documentation/memory-hotplug.txt > @@ -138,10 +138,7 @@ is described under /sys/devices/system/memory as > /sys/devices/system/memory/memoryXXX > (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 > @@ -155,16 +152,14 @@ This device covers address range [0x100000000 ... 0x140000000) > Under each memory block, you can see 4 or 5 files, the end_phys_index file > being a recent addition and not present on older kernels. > > -/sys/devices/system/memory/memoryXXX/start_phys_index > +/sys/devices/system/memory/memoryXXX/phys_index > /sys/devices/system/memory/memoryXXX/end_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. > +'end_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", > -- > > Not sure whether it is proper to remove end_phys_index, too? If we are going to leave the code as it is today such that the start_phys_index and end_phys_index files both contain the same value I don't see why we should not do this. Li Zhong, unless anyone has objections, can you submit a patch to update the files in sysfs and the documentation? -Nathan > > Thanks, > Zhong > > > > >> >> -Nathan >> --- >> Documentation/memory-hotplug.txt | 113 ++++++++++++++++++++------------------- >> 1 file changed, 59 insertions(+), 54 deletions(-) >> >> Index: linux/Documentation/memory-hotplug.txt >> =================================================================== >> --- linux.orig/Documentation/memory-hotplug.txt >> +++ linux/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. >> + >> +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 of sections, please read this file: >> +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 >> @@ -123,14 +128,15 @@ 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 >> @@ -141,13 +147,13 @@ range. Currently there is no way to dete >> 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 or 5 files, the end_phys_index file >> +being a recent addition and not present on older kernels. >> >> /sys/devices/system/memory/memoryXXX/start_phys_index >> /sys/devices/system/memory/memoryXXX/end_phys_index >> @@ -185,6 +191,7 @@ For example: >> A backlink will also be created: >> /sys/devices/system/memory/memory9/node0 -> ../../node/node0 >> >> + >> -------------------------------- >> 4. Physical memory hot-add phase >> -------------------------------- >> @@ -227,11 +234,10 @@ You can tell the physical address of new >> >> % 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 +246,36 @@ Please see "How to online memory" in thi >> >> 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 +290,22 @@ 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 +321,27 @@ 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 +378,11 @@ 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 +418,8 @@ 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. > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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