On Wed, 31 Mar 2010 17:51:57 +0900 KAMEZAWA Hiroyuki wrote:
> Added more changes since v1.
> I'm not in hurry, please see when you have free time.
OK, I have some comments for you to consider.
> ==
> Documentation update. We have too much files now....
>
> Changlog:
> - added memory.soft_limit_in_bytes to summary.
> - rewrite Testing section
> - fixed text about page_cgroup allocation
> - passed aspell(1) ;)
> - rewrote Locking section
> - update memory.stat file explanation
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> Documentation/cgroups/memory.txt | 187 ++++++++++++++++++++++++++++-----------
> 1 file changed, 139 insertions(+), 48 deletions(-)
>
> Index: mmotm-2.6.34-Mar24/Documentation/cgroups/memory.txt
> ===================================================================
> --- mmotm-2.6.34-Mar24.orig/Documentation/cgroups/memory.txt
> +++ mmotm-2.6.34-Mar24/Documentation/cgroups/memory.txt
> @@ -33,6 +23,45 @@ d. A CD/DVD burner could control the amo
> 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-mmotom(development version of 2010/March)
-mmotm
> +
> +Features:
> + - accounting anonymous pages, file caches, swap caches usage and limit 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)
> + cgroup.procs # attach a process(all threads under it)
> + 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 hit limits
> + memory.memsw.failcnt # show the number of memory+Swap hit 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 +135,14 @@ the necessary data structures and check
> 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 never be reclaimable and will not be on global LRU
Awkward sentence above. Maybe:
Some pages which are never reclaimable and will not be on the global LRU
> +are not accounted. we just accounts pages under usual vm management.
We just account
Prefer "VM" to "vm". (multiple places)
>
> 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
> @@ -121,7 +150,12 @@ inserted into inode (radix-tree). While
> 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), it may exist as SwapCache in the system until it really
they they are really
> +freed. Such SwapCache is also accounted. Swapped-in pages are not accounted
> +until it's mapped. This is because of swapin-readahead.
they are mapped.
> +
> +A Cache pages is unaccounted when it's removed from inode (radix-tree).
page
>
> At page migration, accounting information is kept.
>
> @@ -143,6 +177,7 @@ caller of swapoff rather than the users
>
>
> 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.
>
> @@ -150,9 +185,15 @@ When swap is accounted, following files
> - 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 mem+swap is limited by memsw.limit_in_bytes.
OK, you define "memsw" as memory+swap, then use "mem+swap". Is that the
same thing? If so, I would use one of the first 2 choices and drop the last one
instead of having 3 phrases that mean the same thing.
>
> -* 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.
> +(bad process will cause OOM under the memcg. you can avoid system OOM because
Bad You
> + of no swap.)
> +
> +* 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
> @@ -168,12 +209,12 @@ 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
> @@ -189,11 +230,17 @@ When oom event notifier is registered, e
>
> 2. 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.
following:
> + PG_locked.
> + mm->page_table_lock
> + zone->lru_lock
> + lock_page_cgroup.
> + In many case, just lock_page_cgroup() is called.
cases,
> + per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
> + zone->lru_lock, it has no its own lock.
it has no lock of its own.
>
> 3. User Interface
>
> @@ -202,6 +249,7 @@ The memory controller uses the following
> 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
> @@ -216,16 +264,14 @@ 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 is Kibibytes, Mebibytes, Gibibytes)
are ...bytes.)
> +
> 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
> @@ -248,15 +294,24 @@ caches, RSS and Active pages/Inactive pa
>
> 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 feature and implementation, see memcg_test.txt.
features
> +
> +Performance test is also important. To see pure memcg's overhead,
> +testing om tmpfs will give you good numbers of small overheads.
> +example) do kernel make on tmpfs.
Example:
> +
> +Page-fault scalability is also important. At measuring pararell
parallel
> +page fault test, multi-process test may be better than multi-thread
> +test because multi-thread shares something and need sync.
> +
> +But above 2 is testing extreme situation. Trying usual test under memcg
> +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
> @@ -264,6 +319,9 @@ terminated. There are several causes for
> 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
insert space: 10. OOM Control
> +see what happens will be a help.
seeing what happens will be helpful.
> +
> 4.2 Task migration
>
> When a task migrates from one cgroup to another, it's charge is not
> @@ -271,16 +329,19 @@ carried forward by default. The pages al
> 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 its parent. At moving, both of RSS
their
> +and CACHES are moved to parent.
> +rmdir() may return -EBUSY if freeing/moving fails. See 5.1 Also.
also.
>
> Charges recorded in swap information is not updated at removal of cgroup.
> Recorded information is discarded and a cgroup which uses swap (swapcache)
> @@ -309,19 +370,41 @@ will be charged as a new owner of it.
>
> memory.stat file includes following statistics
>
> +# per-memcg 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
> + lru list.
> +active_anon - # of bytes of anonymous and swap cache memory on active
> 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.
> +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 memcg is
> +hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to
> + hierarchy under which memcg 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)
> @@ -337,17 +420,25 @@ Memo:
> 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 amoung other cgroups. In that case,
> + file_mapped is accounted only when the memcg 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 it has other cgroup(s) below it.
> - a cgroup which uses hierarchy and not the root of hierarchy.
>
> +5.4 failcnt
> +
> +The memory controller provides memory.failcnt and memory.memsw.failcnt files.
> +This failcnt(== failure count) shows the number of events that usage counter
shows the number of times that a usage counter
> +hit limits. When a memory controller hit limit, failcnt increase and memory
hit its limit. When a memory controller hits a limit, failcnt increases and memory
> +under it will be reclaimed.
>
> 6. Hierarchy support
>
HTH.
---
~Randy
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