On Tue, 22 Jan 2013 17:47:37 +0400 Glauber Costa <glommer@xxxxxxxxxxxxx> wrote: > This patch is a preparatory work for later locking rework to get rid of > big cgroup lock from memory controller code. Is this complete? From my reading, the patch is also a bugfix. It prevents stale tunable values from getting installed into new children? > The memory controller uses some tunables to adjust its operation. Those > tunables are inherited from parent to children upon children > intialization. For most of them, the value cannot be changed after the > parent has a new children. > > cgroup core splits initialization in two phases: css_alloc and css_online. > After css_alloc, the memory allocation and basic initialization are > done. But the new group is not yet visible anywhere, not even for cgroup > core code. It is only somewhere between css_alloc and css_online that it > is inserted into the internal children lists. Copying tunable values in > css_alloc will lead to inconsistent values: the children will copy the > old parent values, that can change between the copy and the moment in > which the groups is linked to any data structure that can indicate the > presence of children. That describes the problem, but not the fix. Don't we need something like "therefore move the propagation of tunables into the css_online handler". What remains unclear is how we prevent races during the operation of the css_online handler. Suppose mem_cgroup_css_online() is mid-execution and userspace comes in and starts modifying the parent's tunables? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>