On Wed, 28 Feb 2024 at 21:01, Mathieu Desnoyers
[off-list ref] wrote:
[...]

AFAIK the only project using the mm_cid concept I know of today is
tcmalloc. It's very useful to scale data structures such as memory
allocator arenas to the number of concurrently running threads
within a process without having to rely on heuristics on the
user-space side.

I have plans to migrate LTTng-UST to per-ipc-namespace NUMA-aware
mm_cid as well (after I get around to submit this extension into the
Linux kernel) for user-space ring buffers over shared memory, but my
current focus has been on pushing support for extensible RSEQ into
GNU libc for the past year or so.

We are getting there though:

https://sourceware.org/pipermail/libc-alpha/2024-February/154390.html

Glad to see this!

Once we have this key piece in place within GNU libc, it will become
easier to extend rseq further because the libc will adapt to the extended
feature set.

Note that the overhead of the mm_cid assignment within the scheduler
should be negligible after
commit 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid").

Another thing we've actively been working on is to get the "librseq"
project [1] in shape so a copy the librseq headers can be integrated
into the GNU libc project as internal header files. So basically
librseq will become a GNU libc upstream. This will facilitate
implementation of rseq critical section within GNU libc. One of
the possible use-cases will be to move the GNU libc malloc
implementation to per-mm_cid arenas.

I suppose if GNU libc malloc starts using it then usage would become
ubiquitous in no time.

quoted

I'm aware that TCMalloc was the inspiration for vCPUs [1], then renamed to
CIDs, but am wondering if other users are out there.

I'd be curious to learn about those as well.

I suspect that the lack of official release of librseq critical section
helper headers may contribute to the fact that few applications use advanced
rseq features at this point.

I guess you've answered my question, and I conclude "no known open
source usage yet". A simple search on Github or the likes also didn't
yield anything. I will go and check again in a year or so. ;-)

Thanks,
-- Marco