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Message-Id: <20070822130612.18981.58696.sendpatchset@balbir-laptop> Date: Wed, 22 Aug 2007 18:36:12 +0530 From: Balbir Singh <balbir@...ux.vnet.ibm.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Linux Containers <containers@...ts.osdl.org>, YAMAMOTO Takashi <yamamoto@...inux.co.jp>, Paul Menage <menage@...gle.com>, Dave Hansen <haveblue@...ibm.com>, Linux MM Mailing List <linux-mm@...ck.org>, Nick Piggin <npiggin@...e.de>, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>, Pavel Emelianov <xemul@...nvz.org>, Dhaval Giani <dhaval@...ux.vnet.ibm.com>, Balbir Singh <balbir@...ux.vnet.ibm.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Eric W Biederman <ebiederm@...ssion.com> Subject: [PATCH] Memory controller Add Documentation Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com> --- Documentation/memcontrol.txt | 193 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 193 insertions(+) diff -puN /dev/null Documentation/memcontrol.txt --- /dev/null 2007-06-01 20:42:04.000000000 +0530 +++ linux-2.6.23-rc2-mm2-balbir/Documentation/memcontrol.txt 2007-08-22 18:29:29.000000000 +0530 @@ -0,0 +1,193 @@ +Memory Controller + +0. Salient features + +a. Enable control of both RSS and Page Cache pages +b. The infrastructures 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 container on hitting a limit, reclaims from the per + container LRU + +1. History + +The memory controller has a long history. A request for comments for the memory +controller was posted by Balbir Singh [1]. At the time the RFC was posted +there were several implementations for memory control, the goal of the +RFC was to build consensus and agreement for the minimal features required +for memory control. The first RSS controller was posted by Balbir Singh[2] +in Feb 2007. Pavel Emelianov [3][4][5] has since posted three versions of the +RSS controller. At OLS, at the resource management BoF, everyone suggested +that we handle both page cache and RSS together. Another request was raised +to allow user space handling of OOM. The current memory controller is +at version 6, it combines both RSS and Page Cache Control [11]. + +2. Memory Control + +Memory is a unique resource in the sense that it is present in a limited +amount. If a task requires a lot of CPU processing, the task can spread +its processing over a period of hours, days, months or years, but with +memory, the same physical memory needs to be reused to accomplish the task. + +The memory controller implementation has been divided into phases, these +are + +1. Memory controller +2. mlock(2) controller +3. Kernel user memory accounting and slab control +4. user mappings length controller + +The memory controller is the first controller developed. + +2.1. Design + +The core of the design is a counter called the res_counter. The res_counter +tracks the current memory usage and limit of the group of processes associated +with the controller. Each container has a memory controller specific data +structure (mem_container) associated with it. + +2.2. Accounting + + +--------------------+ + | mem_container | + | (res_counter) | + +--------------------+ + / ^ \ + / | \ + +---------------+ | +---------------+ + | mm_struct | |.... | mm_struct | + | | | | | + +---------------+ | +---------------+ + | + + --------------+ + | + +---------------+ +------+--------+ + | page +----------> page_container| + | | | | + +---------------+ +---------------+ + + (Figure 1: Hierarchy of Accounting) + + +Figure 1 shows the important aspects of the controller + +1. Accounting happens per container +2. Each mm_struct knows about which container they belong to +3. Each page has a pointer to the page_container, which in turn knows the + container it belongs to + +The accounting is done as follows, mem_container_charge() is invoked to setup +the necessary data structures and check if the container that is being charged +is over its limit. If it is then reclaim is invoked on the container. +More details can be found in the reclaim section of this document. +If everything goes well, a page meta-data-structure called page_container is +allocated and associated with the page. This routine also adds the page to +the per container LRU. + +2.3 Shared Page Accounting + +Shared pages are accounted on the basis of the first touch approach. The +container that first touches a page is accounted for the page. The principle +behind this approach is that a container that aggressively uses a shared +page, will eventually get charged for it (once it is uncharged from +the container that brought it in -- this will happen on memory pressure). + +2.4 Reclaim + +Each container maintains a per container LRU that consists of an active +and inactive list. When a container goes over its limit, we first try +and reclaim memory from the container so as to make space for the new +pages that the container has touched. If the reclaim is unsuccessful, +an OOM routine is invoked to select and kill the bulkiest task in the +container. + +The reclaim algorithm has not been modified for containers, except that +pages that are selected for reclaiming come from the per container LRU +list. + +2.5 + +3. User Interface + +0. Configuration + +a. Enable CONFIG_CONTAINERS +b. Enable CONFIG_RESOURCE_COUNTERS +c. Enable CONFIG_CONTAINER_MEM_CONT + +1. Prepare the containers +# mkdir -p /containers +# mount -t container none /containers -o memory + +2. Make the new group and move bash into it +# mkdir /containers/0 +# echo $$ > /containers/0/tasks + +Since now we're in the 0 container. +We can alter the memory limit +# echo -n 6000 > /containers/0/memory.limit + +We can check the usage +# cat /containers/0/memory.usage +25 + +The memory.failcnt gives the number of times that the container limit was +exceeded. + +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. + +4.1 Troubleshooting + +Sometimes a user might find that the application under a container is +terminated, there are several causes for this + +1. The container 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 + +echo 1 > /proc/sys/vm/drop_pages will help get rid of some of the pages +cached in the container (page cache pages). + +5. TODO + +1. Add support for accounting huge pages (as a separate controller) +2. Improve the user interface to accept/display memory limits in KB or MB + rather than pages (since page sizes can differ across platforms/machines). +3. Make container lists per-zone +4. Make per-container scanner reclaim not-shared pages first +5. Teach controller to account for shared-pages +6. Start reclamation when the limit is lowered +7. Start reclamation in the background when the limit is + not yet hit but the usage is getting closer +8. Create per zone LRU lists per container + +Summary + +Overall, the memory controller has been a stable controller and has been +commented and discussed on quite extensively in the community. + +References + +1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/ +2. Singh, Balbir. Memory Controller (RSS Control), + http://lwn.net/Articles/222762/ +3. Emelianov, Pavel. Resource controllers based on process containers + http://lkml.org/lkml/2007/3/6/198 +4. Emelianov, Pavel. RSS controller based on process containers (v2) + http://lkml.org/lkml/2007/4/9/74 +5. Emelianov, Pavel. RSS controller based on process containers (v3) + http://lkml.org/lkml/2007/5/30/244 +6. Menage, Paul. Containers v10, http://lwn.net/Articles/236032/ +7. Vaidyanathan, Srinivasan, Containers: Pagecache accounting and control + subsystem (v3), http://lwn.net/Articles/235534/ +8. Singh, Balbir. RSS controller V2 test results (lmbench), + http://lkml.org/lkml/2007/5/17/232 +9. Singh, Balbir. RSS controller V2 AIM9 results + http://lkml.org/lkml/2007/5/18/1 +10. Singh, Balbir. Memory controller v6 results, + http://lkml.org/lkml/2007/8/19/36 +11. Singh, Balbir. Memory controller v6, http://lkml.org/lkml/2007/8/17/69 _ -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL - 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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