On Fri, Oct 27, 2017 at 4:31 PM, Eric Wheeler [off-list ref] wrote:

quoted

Seems like something that's a lot of effort for little gain.  It'll
only help when A) everything you need isn't dirty, and

Indeed!

quoted

B) all the associated btree nodes are in memory.

Is the dirty key map not memory resident?

The overall bcache btree says where stuff is resident and whether it's
dirty.  It is stored on disk and portions of it are cached in memory.

If data is hot, the relevant tree nodes are likely to be in memory,
but the data is also more likely to be dirty.

Mike