So if we call the OOM killer early, do we still get races?

I think the point is that if the Kernel doesn't have 32KiB of clean pages left to dealloc, then from the point of an ordinary desktop, the system has already failed. It would already be unusable.

It is very hard to know *exactly* how much memory is needed to free a page. However, even on a low end 2GB netbook, and even if we reserve only 1% of ram for clean pages (and emergency allocations) that still allows a lot of "too small to fail" allocations. On most systems, reserving 10% would seem reasonable. On embedded systems without a disk it may not make much sense, but they may still have a use for Transcendent/ephemeral memory (and they probably aren't using XFS anyway).