Squash revert of:

Revert "lib/int_sqrt.c: optimize square root algorithm"

This reverts commit 589409794dfb0ab1ba26ac1dc362b51665334128.

Revert "writeback: Fix occasional slow sync(1)"

This reverts commit abae24e6cefe6db04a541e01049028d15ee14431.

Revert "Input: Send events one packet at a time"

This reverts commit 755b6f615b52279ea368c13378009520037e4c73.

Revert "writeback: fix writeback cache thrashing"

This reverts commit b2bbc6dc81f50b27919e0a9ee5c937af662193cc.

Revert "mm: pass readahead info down to the i/o scheduler"

This reverts commit 53b865b57645ad17e2421166d8be7764c7f483b8.