KS2009: How Google uses Linux

1) sched_yield with CFS trouble
Does the /proc/sys/kernel/sched_compat_yield flag help? This is the third time I've ran into sched_yield() behavior issues in the last couple weeks, all related to userspace locking. I'd really like to know what we (kernel developers) can do to make this recurring problem go away. Big applications often seem to have need of better performing locking constructs. Adaptive mutexes, implemented with futexes, seem like they could address a lot of this, with a couple exceptions: the spin time is not user configurable AFAIK, the additional accounting, etc. done in support of POSIX seems to make even the uncontended calls into glibc too expensive. A common response seems to be that userspace locking isn't the right answer and they should rely on OS primitives. Unfortunately, as Chris Wright mentioned during Day 1, these developers of empirical evidence to the contrary. I was reviewing some for a different project today, sometimes the performance difference is staggering.

2) Mike asked why the kernel tries so hard to allocate memory - why not just fail to allocate if there is too much pressure. Why isn't disabling overcommit enough?