On Thu, 15 Feb 2024 18:51:41 -0500
Kent Overstreet [off-list ref] wrote:

Most of that is data (505024), not text (68582, or 66k).

And the 4K extra would have been data too.

The data is mostly the alloc tags themselves (one per allocation
callsite, and you compiled the entire kernel), so that's expected.

Of the text, a lot of that is going to be slowpath stuff - module load
and unload hooks, formatt and printing the output, other assorted bits.

Then there's Allocation and deallocating obj extensions vectors - not
slowpath but not super fast path, not every allocation.

The fastpath instruction count overhead is pretty small
 - actually doing the accounting - the core of slub.c, page_alloc.c,
   percpu.c
 - setting/restoring the alloc tag: this is overhead we add to every
   allocation callsite, so it's the most relevant - but it's just a few
   instructions.

So that's the breakdown. Definitely not zero overhead, but that fixed
memory overhead (and additionally, the percpu counters) is the price we
pay for very low runtime CPU overhead.

But where are the benchmarks that are not micro-benchmarks. How much
overhead does this cause to those? Is it in the noise, or is it noticeable?

-- Steve