[$] Measuring and improving buffered I/O

There are two types of file I/O on Linux, buffered I/O, which goes through
the page cache, and direct I/O, which goes directly to the storage device.
The performance of buffered I/O was reported to be a lot worse than direct
I/O, especially for one specific test, in Luis Chamberlain's
topic
proposal for a session at the 2024 Linux Storage,
Filesystem, Memory Management, and BPF Summit.
The proposal resulted in a lengthy mailing-list discussion,
which also came up in Paul McKenney's RCU session the next
day; Chamberlain led a
combined storage and filesystem session to discuss those results with an
eye toward improving buffered I/O performance.