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From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: "Георгий Кириченко" <georgy@tarantool.org>,
	tarantool-patches@freelists.org
Subject: Re: [RFC v3] fiber: Increase default stack size
Date: Tue, 26 Feb 2019 14:16:32 +0300	[thread overview]
Message-ID: <20190226111632.GM7198@uranus> (raw)
In-Reply-To: <20190226102656.gwwy35jyaqdkci3l@esperanza>

On Tue, Feb 26, 2019 at 01:26:56PM +0300, Vladimir Davydov wrote:
...
> 
> Talked to Kostja and Georgy. We agreed on the following points:
> 
>  - Regarding slab poisoning. We don't want to implement ad hoc allocator
>    for fiber stacks, neither do we really want to patch the small lib
>    for now. Let's use madvise(MADV_DONTNEED) for all fiber stacks
>    unconditionally on fiber creation. This should be okay from
>    performance point of view, because once a fiber is created, it's
>    never destroyed - it stays on the dead list until recycled.

OK

>  - 1 MB for max stack size seems to be a bit of an overkill for now.
>    The default value should be set to 256 KB, but we do need a
>    configuration option for it. Let's add it to the fiber Lua module.
>    May be done in a separate patch, but should be submitted together in
>    the same patch set.

Wait, first fiber for main cord is created before lua init, isn't it?
I already though about using lua config for it but fiber init'ed at
very early stage.

>  - 16 byte unique identifier for detecting stack overflow doesn't seem
>    to be enough. Imagine a PATH_MAX buffer allocated on stack that uses
>    only a hundred bytes for path formatting. It can easily jump over the
>    watermark. We should probably use random poisoning: say, 4 unique
>    identifiers 8 bytes each scattered a few hundred bytes apart. Some
>    math/reasoning behind this would be nice to see in the comments.

If we want to scatter we should simply put marks at page bounds.
Dirtifying somewhere inside middle of a page is useless.

>  - Since madvise() is somewhat expensive to be called on each fiber
>    recycle, we need to make the watermark dynamic. That is, keep track
>    of the number of fibers that have exceeded the watermark and when
>    there are too many of those, increase the watermark value. We could
>    probably use a histogram for this. This would allow us to decrease
>    the default stack allocation size from 64 KB down to 16 KB, which
>    would be really nice. This should be done in a separate patch, but
>    again in the scope of this issue.

Nod.

> 
>  - We definitely need this patch (or patches) to be covered with unit
>    tests. Please add corresponding cases to test/unit/fiber.cc.

Yes, need to address this too. Thanks a huge for comments!

	Cyrill

  parent reply	other threads:[~2019-02-26 11:16 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-22 20:16 [tarantool-patches] [RFC v2] " Cyrill Gorcunov
2019-02-25 14:55 ` Vladimir Davydov
2019-02-25 15:25   ` Cyrill Gorcunov
2019-02-25 21:39   ` [RFC v3] " Cyrill Gorcunov
2019-02-26  8:58     ` Vladimir Davydov
2019-02-26  9:12       ` Cyrill Gorcunov
2019-02-26 10:26         ` Vladimir Davydov
2019-02-26 10:36           ` Vladimir Davydov
2019-02-26 11:17             ` Cyrill Gorcunov
2019-02-26 12:25               ` Vladimir Davydov
2019-02-26 11:16           ` Cyrill Gorcunov [this message]
2019-02-26 12:34             ` Vladimir Davydov
2019-02-26 12:54               ` Cyrill Gorcunov
2019-02-26 13:06                 ` Vladimir Davydov
2019-02-26 13:26               ` [tarantool-patches] " Konstantin Osipov
2019-02-26 14:02                 ` Cyrill Gorcunov
2019-02-26 10:32     ` Vladimir Davydov
2019-02-26 11:18       ` Cyrill Gorcunov

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