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Re: [dm-devel] btree vs. linear seach in device mapper



On Thu, Apr 04, 2013 at 10:27:02AM -0400, Mikulas Patocka wrote:
> BTW. when I see that btree code in dm-table.c, I ask - why doesn't it use 
> binary search?
> 
> We only append targets at the end when constructing the device, we never 
> insert or remove them, so we don't need a tree. For these operations 
> binary search would be as good as btree and it is simpler.

I originally expected dm tables to have many, many more entries than
they do these days (I remember benchmarking it with 1 million
entries).  I used a btree to try and be nicer to the cpu cache; the
idea being that each btree node could fit into a cache line.  Plain
binary search would have caused many more cache faults.

Given how dm is used these days I wouldn't mind a switch to a binary
search.

- Joe


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