[PATCH 2/2] lib/core/fiber: Allow to extend default stack size
Vladimir Davydov
vdavydov.dev at gmail.com
Wed Mar 27 13:15:52 MSK 2019
On Wed, Mar 27, 2019 at 12:46:18PM +0300, Cyrill Gorcunov wrote:
> On Wed, Mar 27, 2019 at 12:35:06PM +0300, Vladimir Davydov wrote:
> > > diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
> > > index 922a0bfe8..d3cb18a15 100644
> > > --- a/src/lib/core/fiber.c
> > > +++ b/src/lib/core/fiber.c
> > > @@ -107,18 +107,25 @@ pthread_t main_thread_id;
> > > static size_t page_size;
> > > static bool stack_growsdown;
> > >
> > > +/** Indices in fiber stack sizes (FSS) */
> > > enum {
> > > + FSS_IDX_MINIMAL,
> > > + FSS_IDX_WATERMARK,
> > > + FSS_IDX_DEFAULT,
> > > +};
> > > +
> > > +/** Fiber stack sizes */
> > > +static size_t fiber_stack_size[] = {
> > > /* The minimum allowable fiber stack size in bytes */
> > > - FIBER_STACK_SIZE_MINIMAL = 16384,
> > > + [FSS_IDX_MINIMAL] = 16384,
> > > + /* Stack size watermark in bytes */
> > > + [FSS_IDX_WATERMARK] = 65536,
> > > /* Default fiber stack size in bytes */
> > > - FIBER_STACK_SIZE_DEFAULT = 524288,
> > > - /* Stack size watermark in bytes. */
> > > - FIBER_STACK_SIZE_WATERMARK = 65536,
> > > + [FSS_IDX_DEFAULT] = 524288,
> > > };
> >
> > Please avoid unrelated changes. If you want to rename or refactor
> > something, do it in a separate patch to ease review.
> >
> > Anyway, I don't see much point in this change - in Tarantool code it's
> > common to use a enum for storing constants.
>
> These are not constants anymore since we're to ajust the values.
Ah, I see. Anyway, I'd leave the constants alone and instead introduce a
separate static variable to store the current stack size in, because
mixing constants (min_size, watermark) and variables (current_default)
in one array doesn't look good to me.
>
> > > +/**
> > > + * Initialize early parameters of the stack
> > > + * and setup default variables.
> > > + */
> > > +static void
> > > +fiber_stack_init(void)
> > > +{
> > > + static const char default_size_name[] = "FIBER_STACK_SIZE_DEFAULT";
> >
> > There's a risk it may conflict with another environment variable.
> > At the very least, we should prefix it with TARANTOOL_.
> >
> > However, I don't think that using an environmental variable is a proper
> > way to go. After all, Tarantool is an application server so we typically
> > set system variables right from Lua code.
> >
> > Can we introduce a function in the fiber module for this? The tricky
> > part is that it should change the stack size of the calling fiber,
> > I guess.
>
> Yes, stacks are allocated earlier, and we simply can't adjust already
> allocated stack thus we might need to distinguish stack sizes between
> cord_main and new fibers. This gonna be hard and I would like to escape
> such complexity. Seriously, we should use a hard rule: every stack in
> the engine has the same size allocated.
>
> Lets think -- is there a chance we will have to provide more configurable
> settings for early init stage in future? If yes then we should invent
> early init stage for lua (or say some json fine in /etc). If no and
> there is no chance we might need something else in future, better to
> stick with simplier solution as environment variables.
Makes sense. But as this is a change in the API, we should consult
Kostja (Cc-ed).
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