There also seems to have been pretty severe performance regressions in
cache bypassed sequential I/O.
The newer code barely does 70mb/s sequential writes when
sequential_cuttoff is set to 4M however it does around 300mb/s when
set to 0 (no bypass) with dd and 1M block size.
When using the older codebase the cache bypass is actually slightly
faster than going to cache at around 360mb/s but this is still much
slower than the underlying block devices (as previously discussed).
Joseph.
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