On 09/20/2013 06:25 PM, Gabriel de Perthuis wrote:
SSD […] optimizations (e.g. avoiding unnecessary seek optimizations,
sending writes in clusters, even if they are from unrelated files. This
results in larger write operations and faster write throughput)
The optimisations should be beneficial iff bcache is used in writeback
mode. ssd_spread and discard are enabled separately; I'm not sure what
ssd_spread (from the wiki: more strict about finding a large unused
region of the disk for new allocations) would do for bcache.
From observing iostat I have the impression that bcache sometimes
bypasses the cache, probably related to sequential_cutoff. Seems like
btrfs tries to cluster writes (because an SSD is detected) and next
bcache bypasses the SSD (because the writes are clustered). Doesn't seem
the right kind of cooperation :-)
(Assuming of course that clustered writes are based on sequential writes)
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