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Date: Mon, 11 Mar 2019 11:31:26 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [PATCH 2/2] lib/core/fiber: Mark stack as unneeded on creation
Message-ID: <20190311083126.GG10420@uranus.lan>
References: <20190307213146.1476-1-gorcunov@gmail.com>
 <20190307213146.1476-3-gorcunov@gmail.com>
 <20190311081814.lq3ginhx3rayjwul@esperanza>
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In-Reply-To: <20190311081814.lq3ginhx3rayjwul@esperanza>
To: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: tml <tarantool-patches@freelists.org>, Konstantin Osipov <kostja@tarantool.org>
List-ID: <tarantool-patches.dev.tarantool.org>

On Mon, Mar 11, 2019 at 11:18:14AM +0300, Vladimir Davydov wrote:
> > diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
> > index f16ac873f..a1b261ad4 100644
> > --- a/src/lib/core/fiber.c
> > +++ b/src/lib/core/fiber.c
> > @@ -749,6 +749,14 @@ fiber_stack_create(struct fiber *fiber, size_t stack_size)
> >  	fiber->stack_id = VALGRIND_STACK_REGISTER(fiber->stack,
> >  						  (char *)fiber->stack +
> >  						  fiber->stack_size);
> > +#ifndef TARGET_OS_DARWIN
> > +	/*
> > +	 * We don't expect the whole stack usage in regular
> > +	 * loads, lets try to minimize rss pressure if OS
> > +	 * allows us.
> > +	 */
> > +	madvise(fiber->stack, fiber->stack_size, MADV_DONTNEED);
> > +#endif
> 
> madvise on fiber creation doesn't make much sense without madvise on
> fiber recycling, because fat tasks will quickly fault-in that memory.
> I thought you were going to implement stack shrinking to some predefined
> size (say, allocate 1 MB max, shrink to 64 KB on recycle if watermark
> was overwritten), leaving only dynamic stack sizing for the future (i.e.
> estimating the optimal size to do madvise for basing on average fiber
> stack usage).

Ah. OK, will rework this.