On Sun, Jun 27, 2010 at 10:07 PM, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-06-28 11:03:27]: > >> On Fri, 25 Jun 2010 13:43:45 -0700 >> Greg Thelen <gthelen@xxxxxxxxxx> wrote: >> >> > For the upcoming Linux VM summit, I am interesting in discussing the >> > following proposal. >> > >> > Problem: When tasks from multiple cgroups share files the charging can be >> > non-deterministic. This requires that all such cgroups have unnecessarily high >> > limits. It would be nice if the charging was deterministic, using the file's >> > path to determine which cgroup to charge. This would benefit charging of >> > commonly used files (eg: libc) as well as large databases shared by only a few >> > tasks. >> > >> > Example: assume two tasks (T1 and T2), each in a separate cgroup. Each task >> > wants to access a large (1GB) database file. To catch memory leaks a tight >> > memory limit on each task's cgroup is set. However, the large database file >> > presents a problem. If the file has not been cached, then the first task to >> > access the file is charged, thereby requiring that task's cgroup to have a limit >> > large enough to include the database file. If the order of access is unknown >> > (due to process restart, etc), then all cgroups accessing the file need to have >> > a limit large enough to include the database. This is wasteful because the >> > database won't be charged to both T1 and T2. It would be useful to introduce >> > determinism by declaring that a particular cgroup is charged for a particular >> > set of files. >> > >> > /dev/cgroup/cg1/cg11 # T1: want memory.limit = 30MB >> > /dev/cgroup/cg1/cg12 # T2: want memory.limit = 100MB >> > /dev/cgroup/cg1 # want memory.limit = 1GB + 30MB + 100MB >> > >> > I have implemented a prototype that allows a file system hierarchy be charge a >> > particular cgroup using a new bind mount option: >> > + mount -t cgroup none /cgroup -o memory >> > + mount --bind /tmp/db /tmp/db -o cgroup=/dev/cgroup/cg1 >> > >> > Any accesses to files within /tmp/db are charged to /dev/cgroup/cg1. Access to >> > other files behave normally - they charge the cgroup of the current task. >> > >> >> Interesting, but I want to use madvice() etc..for this kind of jobs, rather than >> deep hooks into the kernel. >> >> madvise(addr, size, MEMORY_RECHAEGE_THIS_PAGES_TO_ME); >> >> Then, you can write a command as: >> >> file_recharge [path name] [cgroup] >> - this commands move a file cache to specified cgroup. >> >> A daemon program which uses this command + inotify will give us much >> flexible controls on file cache on memcg. Do you have some requirements >> that this move-charge shouldn't be done in lazy manner ? >> >> Status: >> We have codes for move-charge, inotify but have no code for new madvise. > > I have not see the approach yet, but ideally one would want to avoid > changing the application, otherwise we are going to get very tightly > bound in the API issues. I agree that changing the application is undesirable. I think the madvise suggestion (above) would not involve changing applications - it would only be used for a manager daemon in response to a inotify as a mechanism change the charge of previously allocated file pages. > I want to understand why do we need bind mounts? I'm not certain that bind mounts are needed. I chose to use bind mounts as a way to create a file system namespace that charged to a particular cgroup. There are other mechanisms. Another approach would be to have a way to dentry attribute (d_cgroup) that is inherited by child dentrys. I tend to prefer the bind mount over the dentry approach because is reduces the number of cgroup references. However, there may be even better ways. > I think this needs more discussion. I agree that more discussion is required. -- Greg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href