diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-firmware-sfi | 15 | ||||
| -rw-r--r-- | Documentation/DMA-API-HOWTO.txt | 85 | ||||
| -rw-r--r-- | Documentation/SubmittingDrivers | 5 | ||||
| -rw-r--r-- | Documentation/cgroups/cgroups.txt | 2 | ||||
| -rw-r--r-- | Documentation/cgroups/memory.txt | 326 | ||||
| -rw-r--r-- | Documentation/devices.txt | 2 | ||||
| -rw-r--r-- | Documentation/feature-removal-schedule.txt | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/Locking | 5 | ||||
| -rw-r--r-- | Documentation/filesystems/squashfs.txt | 32 | ||||
| -rw-r--r-- | Documentation/hwmon/dme1737 | 51 | ||||
| -rw-r--r-- | Documentation/hwmon/lm63 | 7 | ||||
| -rw-r--r-- | Documentation/hwmon/ltc4245 | 4 | ||||
| -rw-r--r-- | Documentation/hwmon/sysfs-interface | 13 | ||||
| -rw-r--r-- | Documentation/hwmon/tmp102 | 26 | ||||
| -rw-r--r-- | Documentation/vm/numa | 186 |
15 files changed, 583 insertions, 186 deletions
diff --git a/Documentation/ABI/testing/sysfs-firmware-sfi b/Documentation/ABI/testing/sysfs-firmware-sfi new file mode 100644 index 000000000000..4be7d44aeacf --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-sfi @@ -0,0 +1,15 @@ +What: /sys/firmware/sfi/tables/ +Date: May 2010 +Contact: Len Brown <lenb@kernel.org> +Description: + SFI defines a number of small static memory tables + so the kernel can get platform information from firmware. + + The tables are defined in the latest SFI specification: + http://simplefirmware.org/documentation + + While the tables are used by the kernel, user-space + can observe them this way: + + # cd /sys/firmware/sfi/tables + # cat $TABLENAME > $TABLENAME.bin diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt index 2e435adfbd6b..98ce51796f71 100644 --- a/Documentation/DMA-API-HOWTO.txt +++ b/Documentation/DMA-API-HOWTO.txt @@ -639,6 +639,36 @@ is planned to completely remove virt_to_bus() and bus_to_virt() as they are entirely deprecated. Some ports already do not provide these as it is impossible to correctly support them. + Handling Errors + +DMA address space is limited on some architectures and an allocation +failure can be determined by: + +- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0 + +- checking the returned dma_addr_t of dma_map_single and dma_map_page + by using dma_mapping_error(): + + dma_addr_t dma_handle; + + dma_handle = dma_map_single(dev, addr, size, direction); + if (dma_mapping_error(dev, dma_handle)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + } + +Networking drivers must call dev_kfree_skb to free the socket buffer +and return NETDEV_TX_OK if the DMA mapping fails on the transmit hook +(ndo_start_xmit). This means that the socket buffer is just dropped in +the failure case. + +SCSI drivers must return SCSI_MLQUEUE_HOST_BUSY if the DMA mapping +fails in the queuecommand hook. This means that the SCSI subsystem +passes the command to the driver again later. + Optimizing Unmap State Space Consumption On many platforms, dma_unmap_{single,page}() is simply a nop. @@ -703,42 +733,25 @@ to "Closing". 1) Struct scatterlist requirements. - Struct scatterlist must contain, at a minimum, the following - members: - - struct page *page; - unsigned int offset; - unsigned int length; - - The base address is specified by a "page+offset" pair. - - Previous versions of struct scatterlist contained a "void *address" - field that was sometimes used instead of page+offset. As of Linux - 2.5., page+offset is always used, and the "address" field has been - deleted. - -2) More to come... - - Handling Errors - -DMA address space is limited on some architectures and an allocation -failure can be determined by: - -- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0 - -- checking the returned dma_addr_t of dma_map_single and dma_map_page - by using dma_mapping_error(): - - dma_addr_t dma_handle; - - dma_handle = dma_map_single(dev, addr, size, direction); - if (dma_mapping_error(dev, dma_handle)) { - /* - * reduce current DMA mapping usage, - * delay and try again later or - * reset driver. - */ - } + Don't invent the architecture specific struct scatterlist; just use + <asm-generic/scatterlist.h>. You need to enable + CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs + (including software IOMMU). + +2) ARCH_KMALLOC_MINALIGN + + Architectures must ensure that kmalloc'ed buffer is + DMA-safe. Drivers and subsystems depend on it. If an architecture + isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in + the CPU cache is identical to data in main memory), + ARCH_KMALLOC_MINALIGN must be set so that the memory allocator + makes sure that kmalloc'ed buffer doesn't share a cache line with + the others. See arch/arm/include/asm/cache.h as an example. + + Note that ARCH_KMALLOC_MINALIGN is about DMA memory alignment + constraints. You don't need to worry about the architecture data + alignment constraints (e.g. the alignment constraints about 64-bit + objects). Closing diff --git a/Documentation/SubmittingDrivers b/Documentation/SubmittingDrivers index 99e72a81fa2f..4947fd8fb182 100644 --- a/Documentation/SubmittingDrivers +++ b/Documentation/SubmittingDrivers @@ -130,6 +130,8 @@ Linux kernel master tree: ftp.??.kernel.org:/pub/linux/kernel/... ?? == your country code, such as "us", "uk", "fr", etc. + http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git + Linux kernel mailing list: linux-kernel@vger.kernel.org [mail majordomo@vger.kernel.org to subscribe] @@ -160,3 +162,6 @@ How to NOT write kernel driver by Arjan van de Ven: Kernel Janitor: http://janitor.kernelnewbies.org/ + +GIT, Fast Version Control System: + http://git-scm.com/ diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index 57444c2609fc..b34823ff1646 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -339,7 +339,7 @@ To mount a cgroup hierarchy with all available subsystems, type: The "xxx" is not interpreted by the cgroup code, but will appear in /proc/mounts so may be any useful identifying string that you like. -To mount a cgroup hierarchy with just the cpuset and numtasks +To mount a cgroup hierarchy with just the cpuset and memory subsystems, type: # mount -t cgroup -o cpuset,memory hier1 /dev/cgroup diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 6cab1f29da4c..7781857dc940 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -1,18 +1,15 @@ Memory Resource Controller NOTE: The Memory Resource Controller has been generically been referred -to as the memory controller in this document. Do not confuse memory controller -used here with the memory controller that is used in hardware. + to as the memory controller in this document. Do not confuse memory + controller used here with the memory controller that is used in hardware. -Salient features - -a. Enable control of Anonymous, Page Cache (mapped and unmapped) and - Swap Cache memory pages. -b. The infrastructure allows easy addition of other types of memory to control -c. Provides *zero overhead* for non memory controller users -d. Provides a double LRU: global memory pressure causes reclaim from the - global LRU; a cgroup on hitting a limit, reclaims from the per - cgroup LRU +(For editors) +In this document: + When we mention a cgroup (cgroupfs's directory) with memory controller, + we call it "memory cgroup". When you see git-log and source code, you'll + see patch's title and function names tend to use "memcg". + In this document, we avoid using it. Benefits and Purpose of the memory controller @@ -33,6 +30,45 @@ d. A CD/DVD burner could control the amount of memory used by the e. There are several other use cases, find one or use the controller just for fun (to learn and hack on the VM subsystem). +Current Status: linux-2.6.34-mmotm(development version of 2010/April) + +Features: + - accounting anonymous pages, file caches, swap caches usage and limiting them. + - private LRU and reclaim routine. (system's global LRU and private LRU + work independently from each other) + - optionally, memory+swap usage can be accounted and limited. + - hierarchical accounting + - soft limit + - moving(recharging) account at moving a task is selectable. + - usage threshold notifier + - oom-killer disable knob and oom-notifier + - Root cgroup has no limit controls. + + Kernel memory and Hugepages are not under control yet. We just manage + pages on LRU. To add more controls, we have to take care of performance. + +Brief summary of control files. + + tasks # attach a task(thread) and show list of threads + cgroup.procs # show list of processes + cgroup.event_control # an interface for event_fd() + memory.usage_in_bytes # show current memory(RSS+Cache) usage. + memory.memsw.usage_in_bytes # show current memory+Swap usage + memory.limit_in_bytes # set/show limit of memory usage + memory.memsw.limit_in_bytes # set/show limit of memory+Swap usage + memory.failcnt # show the number of memory usage hits limits + memory.memsw.failcnt # show the number of memory+Swap hits limits + memory.max_usage_in_bytes # show max memory usage recorded + memory.memsw.usage_in_bytes # show max memory+Swap usage recorded + memory.soft_limit_in_bytes # set/show soft limit of memory usage + memory.stat # show various statistics + memory.use_hierarchy # set/show hierarchical account enabled + memory.force_empty # trigger forced move charge to parent + memory.swappiness # set/show swappiness parameter of vmscan + (See sysctl's vm.swappiness) + memory.move_charge_at_immigrate # set/show controls of moving charges + memory.oom_control # set/show oom controls. + 1. History The memory controller has a long history. A request for comments for the memory @@ -106,14 +142,14 @@ the necessary data structures and check if the cgroup that is being charged is over its limit. If it is then reclaim is invoked on the cgroup. More details can be found in the reclaim section of this document. If everything goes well, a page meta-data-structure called page_cgroup is -allocated and associated with the page. This routine also adds the page to -the per cgroup LRU. +updated. page_cgroup has its own LRU on cgroup. +(*) page_cgroup structure is allocated at boot/memory-hotplug time. 2.2.1 Accounting details All mapped anon pages (RSS) and cache pages (Page Cache) are accounted. -(some pages which never be reclaimable and will not be on global LRU - are not accounted. we just accounts pages under usual vm management.) +Some pages which are never reclaimable and will not be on the global LRU +are not accounted. We just account pages under usual VM management. RSS pages are accounted at page_fault unless they've already been accounted for earlier. A file page will be accounted for as Page Cache when it's @@ -121,12 +157,19 @@ inserted into inode (radix-tree). While it's mapped into the page tables of processes, duplicate accounting is carefully avoided. A RSS page is unaccounted when it's fully unmapped. A PageCache page is -unaccounted when it's removed from radix-tree. +unaccounted when it's removed from radix-tree. Even if RSS pages are fully +unmapped (by kswapd), they may exist as SwapCache in the system until they +are really freed. Such SwapCaches also also accounted. +A swapped-in page is not accounted until it's mapped. + +Note: The kernel does swapin-readahead and read multiple swaps at once. +This means swapped-in pages may contain pages for other tasks than a task +causing page fault. So, we avoid accounting at swap-in I/O. At page migration, accounting information is kept. -Note: we just account pages-on-lru because our purpose is to control amount -of used pages. not-on-lru pages are tend to be out-of-control from vm view. +Note: we just account pages-on-LRU because our purpose is to control amount +of used pages; not-on-LRU pages tend to be out-of-control from VM view. 2.3 Shared Page Accounting @@ -143,6 +186,7 @@ caller of swapoff rather than the users of shmem. 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) + Swap Extension allows you to record charge for swap. A swapped-in page is charged back to original page allocator if possible. @@ -150,13 +194,20 @@ When swap is accounted, following files are added. - memory.memsw.usage_in_bytes. - memory.memsw.limit_in_bytes. -usage of mem+swap is limited by memsw.limit_in_bytes. +memsw means memory+swap. Usage of memory+swap is limited by +memsw.limit_in_bytes. -* why 'mem+swap' rather than swap. +Example: Assume a system with 4G of swap. A task which allocates 6G of memory +(by mistake) under 2G memory limitation will use all swap. +In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap. +By using memsw limit, you can avoid system OOM which can be caused by swap +shortage. + +* why 'memory+swap' rather than swap. The global LRU(kswapd) can swap out arbitrary pages. Swap-out means to move account from memory to swap...there is no change in usage of -mem+swap. In other words, when we want to limit the usage of swap without -affecting global LRU, mem+swap limit is better than just limiting swap from +memory+swap. In other words, when we want to limit the usage of swap without +affecting global LRU, memory+swap limit is better than just limiting swap from OS point of view. * What happens when a cgroup hits memory.memsw.limit_in_bytes @@ -168,12 +219,12 @@ it by cgroup. 2.5 Reclaim -Each cgroup maintains a per cgroup LRU that consists of an active -and inactive list. When a cgroup goes over its limit, we first try +Each cgroup maintains a per cgroup LRU which has the same structure as +global VM. When a cgroup goes over its limit, we first try to reclaim memory from the cgroup so as to make space for the new pages that the cgroup has touched. If the reclaim is unsuccessful, an OOM routine is invoked to select and kill the bulkiest task in the -cgroup. +cgroup. (See 10. OOM Control below.) The reclaim algorithm has not been modified for cgroups, except that pages that are selected for reclaiming come from the per cgroup LRU @@ -184,13 +235,22 @@ limits on the root cgroup. Note2: When panic_on_oom is set to "2", the whole system will panic. -2. Locking +When oom event notifier is registered, event will be delivered. +(See oom_control section) + +2.6 Locking -The memory controller uses the following hierarchy + lock_page_cgroup()/unlock_page_cgroup() should not be called under + mapping->tree_lock. -1. zone->lru_lock is used for selecting pages to be isolated -2. mem->per_zone->lru_lock protects the per cgroup LRU (per zone) -3. lock_page_cgroup() is used to protect page->page_cgroup + Other lock order is following: + PG_locked. + mm->page_table_lock + zone->lru_lock + lock_page_cgroup. + In many cases, just lock_page_cgroup() is called. + per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by + zone->lru_lock, it has no lock of its own. 3. User Interface @@ -199,6 +259,7 @@ The memory controller uses the following hierarchy a. Enable CONFIG_CGROUPS b. Enable CONFIG_RESOURCE_COUNTERS c. Enable CONFIG_CGROUP_MEM_RES_CTLR +d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension) 1. Prepare the cgroups # mkdir -p /cgroups @@ -206,31 +267,28 @@ c. Enable CONFIG_CGROUP_MEM_RES_CTLR 2. Make the new group and move bash into it # mkdir /cgroups/0 -# echo $$ > /cgroups/0/tasks +# echo $$ > /cgroups/0/tasks -Since now we're in the 0 cgroup, -We can alter the memory limit: +Since now we're in the 0 cgroup, we can alter the memory limit: # echo 4M > /cgroups/0/memory.limit_in_bytes NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo, -mega or gigabytes. +mega or gigabytes. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes, Gibibytes.) + NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited). NOTE: We cannot set limits on the root cgroup any more. # cat /cgroups/0/memory.limit_in_bytes 4194304 -NOTE: The interface has now changed to display the usage in bytes -instead of pages - We can check the usage: # cat /cgroups/0/memory.usage_in_bytes 1216512 A successful write to this file does not guarantee a successful set of -this limit to the value written into the file. This can be due to a +this limit to the value written into the file. This can be due to a number of factors, such as rounding up to page boundaries or the total -availability of memory on the system. The user is required to re-read +availability of memory on the system. The user is required to re-read this file after a write to guarantee the value committed by the kernel. # echo 1 > memory.limit_in_bytes @@ -245,15 +303,23 @@ caches, RSS and Active pages/Inactive pages are shown. 4. Testing -Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11]. -Apart from that v6 has been tested with several applications and regular -daily use. The controller has also been tested on the PPC64, x86_64 and -UML platforms. +For testing features and implementation, see memcg_test.txt. + +Performance test is also important. To see pure memory controller's overhead, +testing on tmpfs will give you good numbers of small overheads. +Example: do kernel make on tmpfs. + +Page-fault scalability is also important. At measuring parallel +page fault test, multi-process test may be better than multi-thread +test because it has noise of shared objects/status. + +But the above two are testing extreme situations. +Trying usual test under memory controller is always helpful. 4.1 Troubleshooting Sometimes a user might find that the application under a cgroup is -terminated. There are several causes for this: +terminated by OOM killer. There are several causes for this: 1. The cgroup limit is too low (just too low to do anything useful) 2. The user is using anonymous memory and swap is turned off or too low @@ -261,6 +327,9 @@ terminated. There are several causes for this: A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of some of the pages cached in the cgroup (page cache pages). +To know what happens, disable OOM_Kill by 10. OOM Control(see below) and +seeing what happens will be helpful. + 4.2 Task migration When a task migrates from one cgroup to another, its charge is not @@ -268,16 +337,19 @@ carried forward by default. The pages allocated from the original cgroup still remain charged to it, the charge is dropped when the page is freed or reclaimed. -Note: You can move charges of a task along with task migration. See 8. +You can move charges of a task along with task migration. +See 8. "Move charges at task migration" 4.3 Removing a cgroup A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a cgroup might have some charge associated with it, even though all -tasks have migrated away from it. -Such charges are freed(at default) or moved to its parent. When moved, -both of RSS and CACHES are moved to parent. -If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also. +tasks have migrated away from it. (because we charge against pages, not +against tasks.) + +Such charges are freed or moved to their parent. At moving, both of RSS +and CACHES are moved to parent. +rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also. Charges recorded in swap information is not updated at removal of cgroup. Recorded information is discarded and a cgroup which uses swap (swapcache) @@ -293,10 +365,10 @@ will be charged as a new owner of it. # echo 0 > memory.force_empty - Almost all pages tracked by this memcg will be unmapped and freed. Some of - pages cannot be freed because it's locked or in-use. Such pages are moved - to parent and this cgroup will be empty. But this may return -EBUSY in - some too busy case. + Almost all pages tracked by this memory cgroup will be unmapped and freed. + Some pages cannot be freed because they are locked or in-use. Such pages are + moved to parent and this cgroup will be empty. This may return -EBUSY if + VM is too busy to free/move all pages immediately. Typical use case of this interface is that calling this before rmdir(). Because rmdir() moves all pages to parent, some out-of-use page caches can be @@ -306,19 +378,41 @@ will be charged as a new owner of it. memory.stat file includes following statistics +# per-memory cgroup local status cache - # of bytes of page cache memory. rss - # of bytes of anonymous and swap cache memory. +mapped_file - # of bytes of mapped file (includes tmpfs/shmem) pgpgin - # of pages paged in (equivalent to # of charging events). pgpgout - # of pages paged out (equivalent to # of uncharging events). -active_anon - # of bytes of anonymous and swap cache memory on active - lru list. +swap - # of bytes of swap usage inactive_anon - # of bytes of anonymous memory and swap cache memory on - inactive lru list. -active_file - # of bytes of file-backed memory on active lru list. -inactive_file - # of bytes of file-backed memory on inactive lru list. + LRU list. +active_anon - # of bytes of anonymous and swap cache memory on active + inactive LRU list. +inactive_file - # of bytes of file-backed memory on inactive LRU list. +active_file - # of bytes of file-backed memory on active LRU list. unevictable - # of bytes of memory that cannot be reclaimed (mlocked etc). -The following additional stats are dependent on CONFIG_DEBUG_VM. +# status considering hierarchy (see memory.use_hierarchy settings) + +hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy + under which the memory cgroup is +hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to + hierarchy under which memory cgroup is. + +total_cache - sum of all children's "cache" +total_rss - sum of all children's "rss" +total_mapped_file - sum of all children's "cache" +total_pgpgin - sum of all children's "pgpgin" +total_pgpgout - sum of all children's "pgpgout" +total_swap - sum of all children's "swap" +total_inactive_anon - sum of all children's "inactive_anon" +total_active_anon - sum of all children's "active_anon" +total_inactive_file - sum of all children's "inactive_file" +total_active_file - sum of all children's "active_file" +total_unevictable - sum of all children's "unevictable" + +# The following additional stats are dependent on CONFIG_DEBUG_VM. inactive_ratio - VM internal parameter. (see mm/page_alloc.c) recent_rotated_anon - VM internal parameter. (see mm/vmscan.c) @@ -327,24 +421,37 @@ recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) recent_scanned_file - VM internal parameter. (see mm/vmscan.c) Memo: - recent_rotated means recent frequency of lru rotation. - recent_scanned means recent # of scans to lru. + recent_rotated means recent frequency of LRU rotation. + recent_scanned means recent # of scans to LRU. showing for better debug please see the code for meanings. Note: Only anonymous and swap cache memory is listed as part of 'rss' stat. This should not be confused with the true 'resident set size' or the - amount of physical memory used by the cgroup. Per-cgroup rss - accounting is not done yet. + amount of physical memory used by the cgroup. + 'rss + file_mapped" will give you resident set size of cgroup. + (Note: file and shmem may be shared among other cgroups. In that case, + file_mapped is accounted only when the memory cgroup is owner of page + cache.) 5.3 swappiness - Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. - Following cgroups' swappiness can't be changed. - - root cgroup (uses /proc/sys/vm/swappiness). - - a cgroup which uses hierarchy and it has child cgroup. - - a cgroup which uses hierarchy and not the root of hierarchy. +Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. +Following cgroups' swappiness can't be changed. +- root cgroup (uses /proc/sys/vm/swappiness). +- a cgroup which uses hierarchy and it has other cgroup(s) below it. +- a cgroup which uses hierarchy and not the root of hierarchy. + +5.4 failcnt + +A memory cgroup provides memory.failcnt and memory.memsw.failcnt files. +This failcnt(== failure count) shows the number of times that a usage counter +hit its limit. When a memory cgroup hits a limit, failcnt increases and +memory under it will be reclaimed. + +You can reset failcnt by writing 0 to failcnt file. +# echo 0 > .../memory.failcnt 6. Hierarchy support @@ -363,13 +470,13 @@ hierarchy In the diagram above, with hierarchical accounting enabled, all memory usage of e, is accounted to its ancestors up until the root (i.e, c and root), -that has memory.use_hierarchy enabled. If one of the ancestors goes over its +that has memory.use_hierarchy enabled. If one of the ancestors goes over its limit, the reclaim algorithm reclaims from the tasks in the ancestor and the children of the ancestor. 6.1 Enabling hierarchical accounting and reclaim -The memory controller by default disables the hierarchy feature. Support +A memory cgroup by default disables the hierarchy feature. Support can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup # echo 1 > memory.use_hierarchy @@ -379,10 +486,10 @@ The feature can be disabled by # echo 0 > memory.use_hierarchy NOTE1: Enabling/disabling will fail if the cgroup already has other -cgroups created below it. + cgroups created below it. NOTE2: When panic_on_oom is set to "2", the whole system will panic in -case of an oom event in any cgroup. + case of an OOM event in any cgroup. 7. Soft limits @@ -392,7 +499,7 @@ is to allow control groups to use as much of the memory as needed, provided a. There is no memory contention b. They do not exceed their hard limit -When the system detects memory contention or low memory control groups +When the system detects memory contention or low memory, control groups are pushed back to their soft limits. If the soft limit of each control group is very high, they are pushed back as much as possible to make sure that one control group does not starve the others of memory. @@ -406,7 +513,7 @@ it gets invoked from balance_pgdat (kswapd). 7.1 Interface Soft limits can be setup by using the following commands (in this example we -assume a soft limit of 256 megabytes) +assume a soft limit of 256 MiB) # echo 256M > memory.soft_limit_in_bytes @@ -442,7 +549,7 @@ Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread Note: If we cannot find enough space for the task in the destination cgroup, we try to make space by reclaiming memory. Task migration may fail if we cannot make enough space. -Note: It can take several seconds if you move charges in giga bytes order. +Note: It can take several seconds if you move charges much. And if you want disable it again: @@ -451,21 +558,27 @@ And if you want disable it again: 8.2 Type of charges which can be move Each bits of move_charge_at_immigrate has its own meaning about what type of -charges should be moved. +charges should be moved. But in any cases, it must be noted that an account of +a page or a swap can be moved only when it is charged to the task's current(old) +memory cgroup. bit | what type of charges would be moved ? -----+------------------------------------------------------------------------ 0 | A charge of an anonymous page(or swap of it) used by the target task. | Those pages and swaps must be used only by the target task. You must | enable Swap Extension(see 2.4) to enable move of swap charges. - -Note: Those pages and swaps must be charged to the old cgroup. -Note: More type of pages(e.g. file cache, shmem,) will be supported by other - bits in future. + -----+------------------------------------------------------------------------ + 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) + | and swaps of tmpfs file) mmapped by the target task. Unlike the case of + | anonymous pages, file pages(and swaps) in the range mmapped by the task + | will be moved even if the task hasn't done page fault, i.e. they might + | not be the task's "RSS", but other task's "RSS" that maps the same file. + | And mapcount of the page is ignored(the page can be moved even if + | page_mapcount(page) > 1). You must enable Swap Extension(see 2.4) to + | enable move of swap charges. 8.3 TODO -- Add support for other types of pages(e.g. file cache, shmem, etc.). - Implement madvise(2) to let users decide the vma to be moved or not to be moved. - All of moving charge operations are done under cgroup_mutex. It's not good @@ -473,22 +586,61 @@ Note: More type of pages(e.g. file cache, shmem,) will be supported by other 9. Memory thresholds -Memory controler implements memory thresholds using cgroups notification +Memory cgroup implements memory thresholds using cgroups notification API (see cgroups.txt). It allows to register multiple memory and memsw thresholds and gets notifications when it crosses. To register a threshold application need: - - create an eventfd using eventfd(2); - - open memory.usage_in_bytes or memory.memsw.usage_in_bytes; - - write string like "<event_fd> <memory.usage_in_bytes> <threshold>" to - cgroup.event_control. +- create an eventfd using eventfd(2); +- open memory.usage_in_bytes or memory.memsw.usage_in_bytes; +- write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to + cgroup.event_control. Application will be notified through eventfd when memory usage crosses threshold in any direction. It's applicable for root and non-root cgroup. -10. TODO +10. OOM Control + +memory.oom_control file is for OOM notification and other controls. + +Memory cgroup implements OOM notifier using cgroup notification +API (See cgroups.txt). It allows to register multiple OOM notification +delivery and gets notification when OOM happens. + +To register a notifier, application need: + - create an eventfd using eventfd(2) + - open memory.oom_control file + - write string like "<event_fd> <fd of memory.oom_control>" to + cgroup.event_control + +Application will be notified through eventfd when OOM happens. +OOM notification doesn't work for root cgroup. + +You can disable OOM-killer by writing "1" to memory.oom_control file, as: + + #echo 1 > memory.oom_control + +This operation is only allowed to the top cgroup of sub-hierarchy. +If OOM-killer is disabled, tasks under cgroup will hang/sleep +in memory cgroup's OOM-waitqueue when they request accountable memory. + +For running them, you have to relax the memory cgroup's OOM status by + * enlarge limit or reduce usage. +To reduce usage, + * kill some tasks. + * move some tasks to other group with account migration. + * remove some files (on tmpfs?) + +Then, stopped tasks will work again. + +At reading, current status of OOM is shown. + oom_kill_disable 0 or 1 (if 1, oom-killer is disabled) + under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may + be stopped.) + +11. TODO 1. Add support for accounting huge pages (as a separate controller) 2. Make per-cgroup scanner reclaim not-shared pages first diff --git a/Documentation/devices.txt b/Documentation/devices.txt index 53d64d382343..1d83d124056c 100644 --- a/Documentation/devices.txt +++ b/Documentation/devices.txt @@ -443,6 +443,8 @@ Your cooperation is appreciated. 231 = /dev/snapshot System memory snapshot device 232 = /dev/kvm Kernel-based virtual machine (hardware virtualization extensions) 233 = /dev/kmview View-OS A process with a view + 234 = /dev/btrfs-control Btrfs control device + 235 = /dev/autofs Autofs control device 240-254 Reserved for local use 255 Reserved for MISC_DYNAMIC_MINOR diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt index a86152ae2f6f..672be0109d02 100644 --- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -646,3 +646,13 @@ Who: Thomas Gleixner <tglx@linutronix.de> ---------------------------- +What: old ieee1394 subsystem (CONFIG_IEEE1394) +When: 2.6.37 +Files: drivers/ieee1394/ except init_ohci1394_dma.c +Why: superseded by drivers/firewire/ (CONFIG_FIREWIRE) which offers more + features, better performance, and better security, all with smaller + and more modern code base +Who: Stefan Richter <stefanr@s5r6.in-berlin.de> + +---------------------------- + diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index af1608070cd5..61c98f03baa1 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -429,8 +429,9 @@ check_flags: no implementations. If your fs is not using generic_file_llseek, you need to acquire and release the appropriate locks in your ->llseek(). For many filesystems, it is probably safe to acquire the inode -mutex. Note some filesystems (i.e. remote ones) provide no -protection for i_size so you will need to use the BKL. +mutex or just to use i_size_read() instead. +Note: this does not protect the file->f_pos against concurrent modifications +since this is something the userspace has to take care about. Note: ext2_release() was *the* source of contention on fs-intensive loads and dropping BKL on ->release() helps to get rid of that (we still diff --git a/Documentation/filesystems/squashfs.txt b/Documentation/filesystems/squashfs.txt index b324c033035a..203f7202cc9e 100644 --- a/Documentation/filesystems/squashfs.txt +++ b/Documentation/filesystems/squashfs.txt @@ -38,7 +38,8 @@ Hard link support: yes no Real inode numbers: yes no 32-bit uids/gids: yes no File creation time: yes no -Xattr and ACL support: no no +Xattr support: yes no +ACL support: no no Squashfs compresses data, inodes and directories. In addition, inode and directory data are highly compacted, and packed on byte boundaries. Each @@ -58,7 +59,7 @@ obtained from this site also. 3. SQUASHFS FILESYSTEM DESIGN ----------------------------- -A squashfs filesystem consists of seven parts, packed together on a byte +A squashfs filesystem consists of a maximum of eight parts, packed together on a byte alignment: --------------- @@ -80,6 +81,9 @@ alignment: |---------------| | uid/gid | | lookup table | + |---------------| + | xattr | + | table | --------------- Compressed data blocks are written to the filesystem as files are read from @@ -192,6 +196,26 @@ This table is stored compressed into metadata blocks. A second index table is used to locate these. This second index table for speed of access (and because it is small) is read at mount time and cached in memory. +3.7 Xattr table +--------------- + +The xattr table contains extended attributes for each inode. The xattrs +for each inode are stored in a list, each list entry containing a type, +name and value field. The type field encodes the xattr prefix +("user.", "trusted." etc) and it also encodes how the name/value fields +should be interpreted. Currently the type indicates whether the value +is stored inline (in which case the value field contains the xattr value), +or if it is stored out of line (in which case the value field stores a +reference to where the actual value is stored). This allows large values +to be stored out of line improving scanning and lookup performance and it +also allows values to be de-duplicated, the value being stored once, and +all other occurences holding an out of line reference to that value. + +The xattr lists are packed into compressed 8K metadata blocks. +To reduce overhead in inodes, rather than storing the on-disk +location of the xattr list inside each inode, a 32-bit xattr id +is stored. This xattr id is mapped into the location of the xattr +list using a second xattr id lookup table. 4. TODOS AND OUTSTANDING ISSUES ------------------------------- @@ -199,9 +223,7 @@ it is small) is read at mount time and cached in memory. 4.1 Todo list ------------- -Implement Xattr and ACL support. The Squashfs 4.0 filesystem layout has hooks -for these but the code has not been written. Once the code has been written -the existing layout should not require modification. +Implement ACL support. 4.2 Squashfs internal cache --------------------------- diff --git a/Documentation/hwmon/dme1737 b/Documentation/hwmon/dme1737 index 001d2e70bc11..fc5df7654d63 100644 --- a/Documentation/hwmon/dme1737 +++ b/Documentation/hwmon/dme1737 @@ -9,11 +9,15 @@ Supported chips: * SMSC SCH3112, SCH3114, SCH3116 Prefix: 'sch311x' Addresses scanned: none, address read from Super-I/O config space - Datasheet: http://www.nuhorizons.com/FeaturedProducts/Volume1/SMSC/311x.pdf + Datasheet: Available on the Internet * SMSC SCH5027 Prefix: 'sch5027' Addresses scanned: I2C 0x2c, 0x2d, 0x2e Datasheet: Provided by SMSC upon request and under NDA + * SMSC SCH5127 + Prefix: 'sch5127' + Addresses scanned: none, address read from Super-I/O config space + Datasheet: Provided by SMSC upon request and under NDA Authors: Juerg Haefliger <juergh@gmail.com> @@ -36,8 +40,8 @@ Description ----------- This driver implements support for the hardware monitoring capabilities of the -SMSC DME1737 and Asus A8000 (which are the same), SMSC SCH5027, and SMSC -SCH311x Super-I/O chips. These chips feature monitoring of 3 temp sensors +SMSC DME1737 and Asus A8000 (which are the same), SMSC SCH5027, SCH311x, +and SCH5127 Super-I/O chips. These chips feature monitoring of 3 temp sensors temp[1-3] (2 remote diodes and 1 internal), 7 voltages in[0-6] (6 external and 1 internal) and up to 6 fan speeds fan[1-6]. Additionally, the chips implement up to 5 PWM outputs pwm[1-3,5-6] for controlling fan speeds both manually and @@ -48,14 +52,14 @@ Fan[3-6] and pwm[3,5-6] are optional features and their availability depends on the configuration of the chip. The driver will detect which features are present during initialization and create the sysfs attributes accordingly. -For the SCH311x, fan[1-3] and pwm[1-3] are always present and fan[4-6] and -pwm[5-6] don't exist. +For the SCH311x and SCH5127, fan[1-3] and pwm[1-3] are always present and +fan[4-6] and pwm[5-6] don't exist. The hardware monitoring features of the DME1737, A8000, and SCH5027 are only -accessible via SMBus, while the SCH311x only provides access via the ISA bus. -The driver will therefore register itself as an I2C client driver if it detects -a DME1737, A8000, or SCH5027 and as a platform driver if it detects a SCH311x -chip. +accessible via SMBus, while the SCH311x and SCH5127 only provide access via +the ISA bus. The driver will therefore register itself as an I2C client driver +if it detects a DME1737, A8000, or SCH5027 and as a platform driver if it +detects a SCH311x or SCH5127 chip. Voltage Monitoring @@ -76,7 +80,7 @@ DME1737, A8000: in6: Vbat (+3.0V) 0V - 4.38V SCH311x: - in0: +2.5V 0V - 6.64V + in0: +2.5V 0V - 3.32V in1: Vccp (processor core) 0V - 2V in2: VCC (internal +3.3V) 0V - 4.38V in3: +5V 0V - 6.64V @@ -93,6 +97,15 @@ SCH5027: in5: VTR (+3.3V standby) 0V - 4.38V in6: Vbat (+3.0V) 0V - 4.38V +SCH5127: + in0: +2.5 0V - 3.32V + in1: Vccp (processor core) 0V - 3V + in2: VCC (internal +3.3V) 0V - 4.38V + in3: V2_IN 0V - 1.5V + in4: V1_IN 0V - 1.5V + in5: VTR (+3.3V standby) 0V - 4.38V + in6: Vbat (+3.0V) 0V - 4.38V + Each voltage input has associated min and max limits which trigger an alarm when crossed. @@ -293,3 +306,21 @@ pwm[1-3]_auto_point1_pwm RW Auto PWM pwm point. Auto_point1 is the pwm[1-3]_auto_point2_pwm RO Auto PWM pwm point. Auto_point2 is the full-speed duty-cycle which is hard- wired to 255 (100% duty-cycle). + +Chip Differences +---------------- + +Feature dme1737 sch311x sch5027 sch5127 +------------------------------------------------------- +temp[1-3]_offset yes yes +vid yes +zone3 yes yes yes +zone[1-3]_hyst yes yes +pwm min/off yes yes +fan3 opt yes opt yes +pwm3 opt yes opt yes +fan4 opt opt +fan5 opt opt +pwm5 opt opt +fan6 opt opt +pwm6 opt opt diff --git a/Documentation/hwmon/lm63 b/Documentation/hwmon/lm63 index 31660bf97979..b9843eab1afb 100644 --- a/Documentation/hwmon/lm63 +++ b/Documentation/hwmon/lm63 @@ -7,6 +7,11 @@ Supported chips: Addresses scanned: I2C 0x4c Datasheet: Publicly available at the National Semiconductor website http://www.national.com/pf/LM/LM63.html + * National Semiconductor LM64 + Prefix: 'lm64' + Addresses scanned: I2C 0x18 and 0x4e + Datasheet: Publicly available at the National Semiconductor website + http://www.national.com/pf/LM/LM64.html Author: Jean Delvare <khali@linux-fr.org> @@ -55,3 +60,5 @@ The lm63 driver will not update its values more frequently than every second; reading them more often will do no harm, but will return 'old' values. +The LM64 is effectively an LM63 with GPIO lines. The driver does not +support these GPIO lines at present. diff --git a/Documentation/hwmon/ltc4245 b/Documentation/hwmon/ltc4245 index 02838a47d862..86b5880d8502 100644 --- a/Documentation/hwmon/ltc4245 +++ b/Documentation/hwmon/ltc4245 @@ -72,9 +72,7 @@ in6_min_alarm 5v output undervoltage alarm in7_min_alarm 3v output undervoltage alarm in8_min_alarm Vee (-12v) output undervoltage alarm -in9_input GPIO #1 voltage data -in10_input GPIO #2 voltage data -in11_input GPIO #3 voltage data +in9_input GPIO voltage data power1_input 12v power usage (mW) power2_input 5v power usage (mW) diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface index 3de6b0bcb147..d4e2917c6f18 100644 --- a/Documentation/hwmon/sysfs-interface +++ b/Documentation/hwmon/sysfs-interface @@ -80,9 +80,9 @@ All entries (except name) are optional, and should only be created in a given driver if the chip has the feature. -******** -* Name * -******** +********************* +* Global attributes * +********************* name The chip name. This should be a short, lowercase string, not containing @@ -91,6 +91,13 @@ name The chip name. I2C devices get this attribute created automatically. RO +update_rate The rate at which the chip will update readings. + Unit: millisecond + RW + Some devices have a variable update rate. This attribute + can be used to change the update rate to the desired + frequency. + ************ * Voltages * diff --git a/Documentation/hwmon/tmp102 b/Documentation/hwmon/tmp102 new file mode 100644 index 000000000000..8454a7763122 --- /dev/null +++ b/Documentation/hwmon/tmp102 @@ -0,0 +1,26 @@ +Kernel driver tmp102 +==================== + +Supported chips: + * Texas Instruments TMP102 + Prefix: 'tmp102' + Addresses scanned: none + Datasheet: http://focus.ti.com/docs/prod/folders/print/tmp102.html + +Author: + Steven King <sfking@fdwdc.com> + +Description +----------- + +The Texas Instruments TMP102 implements one temperature sensor. Limits can be +set through the Overtemperature Shutdown register and Hysteresis register. The +sensor is accurate to 0.5 degree over the range of -25 to +85 C, and to 1.0 +degree from -40 to +125 C. Resolution of the sensor is 0.0625 degree. The +operating temperature has a minimum of -55 C and a maximum of +150 C. + +The TMP102 has a programmable update rate that can select between 8, 4, 1, and +0.5 Hz. (Currently the driver only supports the default of 4 Hz). + +The driver provides the common sysfs-interface for temperatures (see +Documentation/hwmon/sysfs-interface under Temperatures). diff --git a/Documentation/vm/numa b/Documentation/vm/numa index e93ad9425e2a..a200a386429d 100644 --- a/Documentation/vm/numa +++ b/Documentation/vm/numa @@ -1,41 +1,149 @@ Started Nov 1999 by Kanoj Sarcar <kanoj@sgi.com> -The intent of this file is to have an uptodate, running commentary -from different people about NUMA specific code in the Linux vm. - -What is NUMA? It is an architecture where the memory access times -for different regions of memory from a given processor varies -according to the "distance" of the memory region from the processor. -Each region of memory to which access times are the same from any -cpu, is called a node. On such architectures, it is beneficial if -the kernel tries to minimize inter node communications. Schemes -for this range from kernel text and read-only data replication -across nodes, and trying to house all the data structures that -key components of the kernel need on memory on that node. - -Currently, all the numa support is to provide efficient handling -of widely discontiguous physical memory, so architectures which -are not NUMA but can have huge holes in the physical address space -can use the same code. All this code is bracketed by CONFIG_DISCONTIGMEM. - -The initial port includes NUMAizing the bootmem allocator code by -encapsulating all the pieces of information into a bootmem_data_t -structure. Node specific calls have been added to the allocator. -In theory, any platform which uses the bootmem allocator should -be able to put the bootmem and mem_map data structures anywhere -it deems best. - -Each node's page allocation data structures have also been encapsulated -into a pg_data_t. The bootmem_data_t is just one part of this. To -make the code look uniform between NUMA and regular UMA platforms, -UMA platforms have a statically allocated pg_data_t too (contig_page_data). -For the sake of uniformity, the function num_online_nodes() is also defined -for all platforms. As we run benchmarks, we might decide to NUMAize -more variables like low_on_memory, nr_free_pages etc into the pg_data_t. - -The NUMA aware page allocation code currently tries to allocate pages -from different nodes in a round robin manner. This will be changed to -do concentratic circle search, starting from current node, once the -NUMA port achieves more maturity. The call alloc_pages_node has been -added, so that drivers can make the call and not worry about whether -it is running on a NUMA or UMA platform. +What is NUMA? + +This question can be answered from a couple of perspectives: the +hardware view and the Linux software view. + +From the hardware perspective, a NUMA system is a computer platform that +comprises multiple components or assemblies each of which may contain 0 +or more CPUs, local memory, and/or IO buses. For brevity and to +disambiguate the hardware view of these physical components/assemblies +from the software abstraction thereof, we'll call the components/assemblies +'cells' in this document. + +Each of the 'cells' may be viewed as an SMP [symmetric multi-processor] subset +of the system--although some components necessary for a stand-alone SMP system +may not be populated on any given cell. The cells of the NUMA system are +connected together with some sort of system interconnect--e.g., a crossbar or +point-to-point link are common types of NUMA system interconnects. Both of +these types of interconnects can be aggregated to create NUMA platforms with +cells at multiple distances from other cells. + +For Linux, the NUMA platforms of interest are primarily what is known as Cache +Coherent NUMA or ccNUMA systems. With ccNUMA systems, all memory is visible +to and accessible from any CPU attached to any cell and cache coherency +is handled in hardware by the processor caches and/or the system interconnect. + +Memory access time and effective memory bandwidth varies depending on how far +away the cell containing the CPU or IO bus making the memory access is from the +cell containing the target memory. For example, access to memory by CPUs +attached to the same cell will experience faster access times and higher +bandwidths than accesses to memory on other, remote cells. NUMA platforms +can have cells at multiple remote distances from any given cell. + +Platform vendors don't build NUMA systems just to make software developers' +lives interesting. Rather, this architecture is a means to provide scalable +memory bandwidth. However, to achieve scalable memory bandwidth, system and +application software must arrange for a large majority of the memory references +[cache misses] to be to "local" memory--memory on the same cell, if any--or +to the closest cell with memory. + +This leads to the Linux software view of a NUMA system: + +Linux divides the system's hardware resources into multiple software +abstractions called "nodes". Linux maps the nodes onto the physical cells +of the hardware platform, abstracting away some of the details for some +architectures. As with physical cells, software nodes may contain 0 or more +CPUs, memory and/or IO buses. And, again, memory accesses to memory on +"closer" nodes--nodes that map to closer cells--will generally experience +faster access times and higher effective bandwidth than accesses to more +remote cells. + +For some architectures, such as x86, Linux will "hide" any node representing a +physical cell that has no memory attached, and reassign any CPUs attached to +that cell to a node representing a cell that does have memory. Thus, on +these architectures, one cannot assume that all CPUs that Linux associates with +a given node will see the same local memory access times and bandwidth. + +In addition, for some architectures, again x86 is an example, Linux supports +the emulation of additional nodes. For NUMA emulation, linux will carve up +the existing nodes--or the system memory for non-NUMA platforms--into multiple +nodes. Each emulated node will manage a fraction of the underlying cells' +physical memory. NUMA emluation is useful for testing NUMA kernel and +application features on non-NUMA platforms, and as a sort of memory resource +management mechanism when used together with cpusets. +[see Documentation/cgroups/cpusets.txt] + +For each node with memory, Linux constructs an independent memory management +subsystem, complete with its own free page lists, in-use page lists, usage +statistics and locks to mediate access. In addition, Linux constructs for +each memory zone [one or more of DMA, DMA32, NORMAL, HIGH_MEMORY, MOVABLE], +an ordered "zonelist". A zonelist specifies the zones/nodes to visit when a +selected zone/node cannot satisfy the allocation request. This situation, +when a zone has no available memory to satisfy a request, is called +"overflow" or "fallback". + +Because some nodes contain multiple zones containing different types of +memory, Linux must decide whether to order the zonelists such that allocations +fall back to the same zone type on a different node, or to a different zone +type on the same node. This is an important consideration because some zones, +such as DMA or DMA32, represent relatively scarce resources. Linux chooses +a default zonelist order based on the sizes of the various zone types relative +to the total memory of the node and the total memory of the system. The +default zonelist order may be overridden using the numa_zonelist_order kernel +boot parameter or sysctl. [see Documentation/kernel-parameters.txt and +Documentation/sysctl/vm.txt] + +By default, Linux will attempt to satisfy memory allocation requests from the +node to which the CPU that executes the request is assigned. Specifically, +Linux will attempt to allocate from the first node in the appropriate zonelist +for the node where the request originates. This is called "local allocation." +If the "local" node cannot satisfy the request, the kernel will examine other +nodes' zones in the selected zonelist looking for the first zone in the list +that can satisfy the request. + +Local allocation will tend to keep subsequent access to the allocated memory +"local" to the underlying physical resources and off the system interconnect-- +as long as the task on whose behalf the kernel allocated some memory does not +later migrate away from that memory. The Linux scheduler is aware of the +NUMA topology of the platform--embodied in the "scheduling domains" data +structures [see Documentation/scheduler/sched-domains.txt]--and the scheduler +attempts to minimize task migration to distant scheduling domains. However, +the scheduler does not take a task's NUMA footprint into account directly. +Thus, under sufficient imbalance, tasks can migrate between nodes, remote +from their initial node and kernel data structures. + +System administrators and application designers can restrict a task's migration +to improve NUMA locality using various CPU affinity command line interfaces, +such as taskset(1) and numactl(1), and program interfaces such as +sched_setaffinity(2). Further, one can modify the kernel's default local +allocation behavior using Linux NUMA memory policy. +[see Documentation/vm/numa_memory_policy.] + +System administrators can restrict the CPUs and nodes' memories that a non- +privileged user can specify in the scheduling or NUMA commands and functions +using control groups and CPUsets. [see Documentation/cgroups/CPUsets.txt] + +On architectures that do not hide memoryless nodes, Linux will include only +zones [nodes] with memory in the zonelists. This means that for a memoryless +node the "local memory node"--the node of the first zone in CPU's node's +zonelist--will not be the node itself. Rather, it will be the node that the +kernel selected as the nearest node with memory when it built the zonelists. +So, default, local allocations will succeed with the kernel supplying the +closest available memory. This is a consequence of the same mechanism that +allows such allocations to fallback to other nearby nodes when a node that +does contain memory overflows. + +Some kernel allocations do not want or cannot tolerate this allocation fallback +behavior. Rather they want to be sure they get memory from the specified node +or get notified that the node has no free memory. This is usually the case when +a subsystem allocates per CPU memory resources, for example. + +A typical model for making such an allocation is to obtain the node id of the +node to which the "current CPU" is attached using one of the kernel's +numa_node_id() or CPU_to_node() functions and then request memory from only +the node id returned. When such an allocation fails, the requesting subsystem +may revert to its own fallback path. The slab kernel memory allocator is an +example of this. Or, the subsystem may choose to disable or not to enable +itself on allocation failure. The kernel profiling subsystem is an example of +this. + +If the architecture supports--does not hide--memoryless nodes, then CPUs +attached to memoryless nodes would always incur the fallback path overhead +or some subsystems would fail to initialize if they attempted to allocated +memory exclusively from a node without memory. To support such +architectures transparently, kernel subsystems can use the numa_mem_id() +or cpu_to_mem() function to locate the "local memory node" for the calling or +specified CPU. Again, this is the same node from which default, local page +allocations will be attempted. |