> On 9 Jan 2020, at 10:47, Willy Tarreau <w...@1wt.eu> wrote:
> 
> Hi Thierry,
> 
> On Thu, Jan 09, 2020 at 10:34:35AM +0100, Thierry Fournier wrote:
>> I'm remember: the execution of the GC were the only way to close TCP 
>> connexions
>> because in some cases the object provided by core.tcp() is not closed and the
>> connexion is not released. Without the GC execution, HAProxy reach the 
>> maximum
>> of available connexion, and the process were blocked. The flag forcing the 
>> GCC
>> is set only is we use a socket.
> 
> Ah OK then it makes sense, thanks for the explanation. However I'm seeing
> that the GC is forced for every yield/resume call, and not just on destroy.
> Maybe it could be acceptable not to call it on resume ?
> 
> Sada, would you be interested in checking if this solves most of the
> performance issue:
> 
> diff --git a/src/hlua.c b/src/hlua.c
> index 37f7866874..e5257efb54 100644
> --- a/src/hlua.c
> +++ b/src/hlua.c
> @@ -1195,7 +1195,7 @@ resume_execution:
>        }
> 
>        /* This GC permits to destroy some object when a Lua timeout strikes. 
> */
> -       if (lua->flags & HLUA_MUST_GC &&
> +       if (0 && lua->flags & HLUA_MUST_GC &&
>            ret ! HLUA_E_AGAIN)
>                lua_gc(lua->T, LUA_GCCOLLECT, 0);


This make sense, but I not remember if the GC at this point is important.

Just for information, there are the commit messages:

    OPTIM/MEDIUM: lua: executes the garbage collector only when using cosocket

    The garbage collector is a little bit heavy to run, and it was added
    only for cosockets. This patch prevent useless executions when no
    cosockets are used.




> 
>> Maybe we try to include new option "tune.lua.forced-gc".
> 
> Based on your description if we need an option, I'd rather have the
> opposite, like "tune.lua.disable-gc" so that it remains enabled by
> default, and with an explanation that one must not disable it.


I agree, but it make sense to run some tests:

 - First, testing your patch to decide if the GC line 1195 is relevant
 - Second, testing the behavior when GC is disabled and lua create connexion 
and lua fail without closing connexion.

Maybe the second case make the GC mandatory.

Thierry


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