Coalescing of disk io requests during merging

grap · 03-02-2011, 04:50 AM

How does coalescing of requests takes place during merging if the following scenario occurs...
say request for sector number 3 and 5 already exists...and a new request for sector 4 arrives, then if it front merges with 5, will it also back merge (i.e coalesce in this case) with 3 ?
if it happens ..which functions are called? and how do we get to know whether a single merge or multiple merges have taken place?

references : blk-core.c, elevator.c, deadline_iosched.c all under /block.

syg00 · 03-02-2011, 10:08 AM

Quote:

Originally Posted by grap

if it happens ..which functions are called?

I'm pretty sure the merging attempts to create as large a consolidated unit as possible. Don't know where it's done though - haven't bothered to look

Quote:

... and how do we get to know whether a single merge or multiple merges have taken place?

For ext, have a look at blktrace - mighty handy for this.