I believe he's referring to Andrea Arcangeli's per-task-predictive-write-throttling.
If I've understood it properly, the patch measures the rate at which each task is writing to disk; if maintaining that rate would cause the kernel to start flushing buffers via pdflush in the near future, the task's timeslice is used to flush instead.
The result is that tasks doing the odd write here and there aren't affected, since they don't cause enough dirty pages. Tasks like cp, which dirty lots of pages, get paused to write out these pages (cleaning them), and making these pages eligible for eviction. This reduces the memory pressure cp-type tasks can induce without killing their performance; cp would eventually pause for the writeout, once it had dirtied as much RAM as it could. The patch just brings this pause forward, so that it doesn't dirty too much RAM before it writes out.
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