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From: Konstantin Osipov <kostja@tarantool.org>
To: tarantool-patches@freelists.org
Cc: gorcunov@gmail.com, vdavydov.dev@gmail.com
Subject: Re: [tarantool-patches] [rfc 4/4] core/fiber: Shrink stack when recycling
Date: Tue, 5 Mar 2019 11:30:48 +0300	[thread overview]
Message-ID: <20190305083048.GM21955@chai> (raw)
In-Reply-To: <20190302130034.125890957@gmail.com>

* Cyrill Gorcunov <gorcunov@gmail.com> [19/03/03 23:25]:
> +#define wmark_freeze(_pp) do { *((uintptr_t *)(_pp)) |= (uintptr_t)1; } while (0)
> +#define wmark_frozen(_p) ((uintptr_t)(_p) & (uintptr_t)1)

Why not static inline? A comment would help. Usually the name for
function returning true/false contains "is", e.g.
wmark_is_frozen().


>  
>  static void
> +stack_shrink(struct fiber *fiber)
> +{
> +	void *hi, *lo;
> +
> +	if (stack_direction < 0) {
> +		hi = fiber->stack + fiber->stack_size;
> +		lo = fiber->stack_wmark_ofl + page_size;
> +	} else {
> +		hi = fiber->stack_wmark_ofl - page_size;
> +		lo = fiber->stack - fiber->stack_size;
> +	}
> +
> +	if (fiber->stack_wmark <= lo ||
> +	    fiber->stack_wmark >= hi)
> +		return;
> +
> +	madvise(fiber->stack_wmark, page_size, MADV_DONTNEED);
> +	if (stack_direction < 0)
> +		fiber->stack_wmark += page_size;
> +	else
> +		fiber->stack_wmark -= page_size;
> +	stack_put_wmark(fiber);
> +}
> +
> +static void
>  fiber_wmark_recycle(struct fiber *fiber)
>  {
>  	static bool overflow_warned = false;
> @@ -772,20 +800,30 @@ fiber_wmark_recycle(struct fiber *fiber)
>  
>  	/*
>  	 * We are watching for stack overflow in one shot way:
> -	 * firstly to not spam a user with messages and secondly
> -	 * to relax system from additional operations while our
> -	 * watermark is not dynamic.
> +	 * to not spam a user with messages.
>  	 */
> -	if (overflow_warned)
> -		return;
> -
> -	if (!stack_has_wmark(fiber->stack_wmark_ofl)) {
> -		if (!overflow_warned) {
> +	if (!overflow_warned) {
> +		if (!stack_has_wmark(fiber->stack_wmark_ofl)) {
>  			say_warn("fiber %d is close to a stack limit",
>  				 fiber->name, fiber->fid);
>  			overflow_warned = true;
>  		}
>  	}
> +
> +	if (wmark_frozen(fiber->stack_wmark))
> +		return;
> +
> +	/*
> +	 * On recycle we're trying to shrink stack
> +	 * as much as we can until first mark overwrite
> +	 * detected, then we simply freeze watermark and
> +	 * assume the stack is balanced and won't change
> +	 * much in future.
> +	 */
> +	if (!stack_has_wmark(fiber->stack_wmark))
> +		wmark_freeze(&fiber->stack_wmark);

I don't see how "frozen" watermark concept is more powerful than
already existing "overflow warned" flag. I think the idea is to
have some sort of smart threshold after which we stop trying to
shrink the stack.

Right now this threshold is not too smart (which is OK), but
complicated (both overflow_warned and wmark_frozen() are
considered), which doesn't make too much sense to me.

> +	else
> +		stack_shrink(fiber);

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov

  reply	other threads:[~2019-03-05  8:30 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-02 12:55 [rfc 0/4] fiber/stack: Increase stack size and shrink rss usage Cyrill Gorcunov
2019-03-02 12:55 ` [rfc 1/4] core/fiber: Increase default stack size Cyrill Gorcunov
2019-03-02 12:55 ` [rfc 2/4] core/fiber: Mark stack as unneeded on creation Cyrill Gorcunov
2019-03-02 12:55 ` [rfc 3/4] core/fiber: Put static watermark into stack to track its usage Cyrill Gorcunov
2019-03-05  8:08   ` [tarantool-patches] " Konstantin Osipov
2019-03-05  8:17     ` Cyrill Gorcunov
2019-03-05  8:10   ` Konstantin Osipov
2019-03-05  8:14     ` Cyrill Gorcunov
2019-03-05 19:17     ` Cyrill Gorcunov
2019-03-05  8:20   ` Konstantin Osipov
2019-03-05  8:27     ` Cyrill Gorcunov
2019-03-02 12:55 ` [rfc 4/4] core/fiber: Shrink stack when recycling Cyrill Gorcunov
2019-03-05  8:30   ` Konstantin Osipov [this message]
2019-03-05  8:41     ` [tarantool-patches] " Cyrill Gorcunov
2019-03-05  9:32       ` [tarantool-patches] " Konstantin Osipov

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