On Fri, Jul 30, 2010 at 4:57 PM, Ben Blum <bblum@xxxxxxxxxxxxxx> wrote: > + * The threadgroup_fork_lock prevents threads from forking with > + * CLONE_THREAD while held for writing. Use this for fork-sensitive > + * threadgroup-wide operations. It's taken for reading in fork.c in > + * copy_process(). > + * Currently only needed write-side by cgroups. > + */ > + struct rw_semaphore threadgroup_fork_lock; > +#endif I'm not sure how best to word this comment, but I'd prefer something like: "The threadgroup_fork_lock is taken in read mode during a CLONE_THREAD fork operation; taking it in write mode prevents the owning threadgroup from adding any new threads and thus allows you to synchronize against the addition of unseen threads when performing threadgroup-wide operations. New-process forks (without CLONE_THREAD) are not affected." As far as the #ifdef mess goes, it's true that some people don't have CONFIG_CGROUPS defined. I'd imagine that these are likely to be embedded systems with a fairly small number of processes and threads per process. Are there really any such platforms where the cost of a single extra rwsem per process is going to make a difference either in terms of memory or lock contention? I think you should consider making these additions unconditional. Paul _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
