[Tarantool-patches] [PATCH 0/2] Reduce Lua GC pressure in Tarantool

[Igor Munkin]

Kirill,

Please proceed with the series.

On 19.06.20, Igor Munkin wrote:
> This series consists of the two patches that seems unrelated. However
> you can look at the CI results[1] for the first incarnation[2] and see
> the reason why the test is also attached.
> 
> The first patch just makes the flaky box-tap/key_def.test.lua stable and
> thereby fixes #4252[3]. The fix is quite simple: since it hits the known
> LuaJIT problem[4] disabling JIT for particular Lua Fun methods is a
> solution for now. When the JIT misbehave is fixed, the patch can be
> reverted. Furthermore, Sasha Tu. asked to open another ticket in our
> queue tracking the origin LuaJIT issue, since #4252 will be closed.
> 
> I failed to find the exact way the patch affects this test, but again,
> the result is in the CI.
> 
> The second patch was born in scope of Sasha L. research[5]. I glanced on
> the flamegraphs and then to the sources and saw no reason why the same
> functions need to be created on each iproto CALL/EVAL or "stored"
> procedure call. These GCfunc objects live only in scope of the coroutine
> (i.e. fiber) serving a request, but can be reused for the others since
> there are no upvalues depending on the request context. As a result of
> the change GC pressure is reduced.
> 
> Vlad asked me personally to make and provide some benchmarks for the
> changes. I made the one you can find here[6]. One need to start
> <callee.lua> instance and run <caller.lua> several times with the same
> Tarantool binary.
> 
> After 15 runs with default args I obtained the following results:
> * Vanilla bleeding master (mean):
> | ===== 2.5.0-147-ge7a70be4e =====
> | call by ref GC: 953127 Kb
> | call by ref time: 1.401803 sec
> | call GC: 507813 Kb
> | eval GC: 686523 Kb
> * Patched bleeding master (mean):
> | ===== 2.5.0-149-g71b2bbc8a =====
> | call by ref GC: 921877 Kb
> | call by ref time: 1.318509 sec
> | call GC: 476563 Kb
> | eval GC: 655273 Kb
> * Relative measurements (before -> after):
> | call by ref GC: -3% (-31250 Kb)
> | call by ref time: -5% (-0.083294 sec)
> | call GC: -6% (-31250 Kb)
> | eval GC: -4% (-31250 Kb)
> 
> Even if one consider benchmarks a bit synthetic, this change improves
> platform performance a priori: as a result less garbage is produced,
> ergo GC machinery is triggered less often.
> 
> Branch: https://github.com/tarantool/tarantool/tree/imun/experimental-execute-lua-handlers
> 
> I guess a ChangeLog entry is irrelevant, since nothing is changed for
> the user space.
> 
> Igor Munkin (2):
>   test: disable JIT for Lua Fun totable function
>   box: reduce box_process_lua Lua GC memory usage
> 
>  src/box/lua/call.c            | 32 +++++++++++++++++++++++++++-----
>  test/box-tap/key_def.test.lua |  8 ++++++++
>  2 files changed, 35 insertions(+), 5 deletions(-)
> 
> [1]: https://gitlab.com/tarantool/tarantool/-/pipelines/138781540/builds
> [2]: https://github.com/tarantool/tarantool/commit/8fe7f00
> [3]: https://github.com/tarantool/tarantool/issues/4252
> [4]: https://github.com/LuaJIT/LuaJIT/issues/584
> [5]: https://github.com/tarantool/vshard/issues/224
> [6]: https://gist.github.com/igormunkin/c941074fa9fdf0f7a4f068498fb5e24c
> 
> -- 
> 2.25.0
> 

-- 
Best regards,
IM