Subject: [PATCH v2 00/11] Request for Inclusion: kmem controller for memcg.
Date: Thursday 9th August 2012 13:01:08 UTC (over 4 years ago)
Hi, This is the first part of the kernel memory controller for memcg. It has been discussed many times, and I consider this stable enough to be on tree. A follow up to this series are the patches to also track slab memory. They are not included here because I believe we could benefit from merging them separately for better testing coverage. If there are any issues preventing this to be merged, let me know. I'll be happy to address them. The slab patches are also mature in my self evaluation and could be merged not too long after this. For the reference, the last discussion about them happened at http://lwn.net/Articles/508087/ A (throwaway) git tree with them is placed at: git://github.com/glommer/linux.git kmemcg-slab A general explanation of what this is all about follows: The kernel memory limitation mechanism for memcg concerns itself with disallowing potentially non-reclaimable allocations to happen in exaggerate quantities by a particular set of processes (cgroup). Those allocations could create pressure that affects the behavior of a different and unrelated set of processes. Its basic working mechanism is to annotate some allocations with the _GFP_KMEMCG flag. When this flag is set, the current process allocating will have its memcg identified and charged against. When reaching a specific limit, further allocations will be denied. One example of such problematic pressure that can be prevented by this work is a fork bomb conducted in a shell. We prevent it by noting that processes use a limited amount of stack pages. Seen this way, a fork bomb is just a special case of resource abuse. If the offender is unable to grab more pages for the stack, no new processes can be created. There are also other things the general mechanism protects against. For example, using too much of pinned dentry and inode cache, by touching files an leaving them in memory forever. In fact, a simple: while true; do mkdir x; cd x; done can halt your system easily because the file system limits are hard to reach (big disks), but the kernel memory is not. Those are examples, but the list certainly don't stop here. An important use case for all that, is concerned with people offering hosting services through containers. In a physical box we can put a limit to some resources, like total number of processes or threads. But in an environment where each independent user gets its own piece of the machine, we don't want a potentially malicious user to destroy good users' services. This might be true for systemd as well, that now groups services inside cgroups. They generally want to put forward a set of guarantees that limits the running service in a variety of ways, so that if they become badly behaved, they won't interfere with the rest of the system. There is, of course, a cost for that. To attempt to mitigate that, static branches are used to make sure that even if the feature is compiled in with potentially a lot of memory cgroups deployed this code will only be enabled after the first user of this service configures any limit. Limits lower than the user limit effectively means there is a separate kernel memory limit that may be reached independently than the user limit. Values equal or greater than the user limit implies only that kernel memory is tracked. This provides a unified vision of "maximum memory", be it kernel or user memory. Because this is all default-off, existing deployments will see no change in behavior. Glauber Costa (9): memcg: change defines to an enum kmem accounting basic infrastructure Add a __GFP_KMEMCG flag memcg: kmem controller infrastructure mm: Allocate kernel pages to the right memcg memcg: disable kmem code when not in use. memcg: propagate kmem limiting information to children memcg: allow a memcg with kmem charges to be destructed. protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs Suleiman Souhlal (2): memcg: Make it possible to use the stock for more than one page. memcg: Reclaim when more than one page needed. include/linux/gfp.h | 10 +- include/linux/memcontrol.h | 82 ++++++++ include/linux/thread_info.h | 2 + kernel/fork.c | 4 +- mm/memcontrol.c | 443 +++++++++++++++++++++++++++++++++++++++++--- mm/page_alloc.c | 38 ++++ 6 files changed, 546 insertions(+), 33 deletions(-) -- 220.127.116.11