Re: [PATCH 3/3] core/fiber: Put watermarks into stack to track its usage

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Thu, Mar 07, 2019 at 11:27:58AM +0300, Vladimir Davydov wrote:
...
> 
> You can track the ratio of fibers that have overwritten the watermark
> recently. If the ratio gets too high (say 90% out of 1000 recently
> scheduled fibers), the minimal stack allocation should be increased.

IOW, we need to gather statistics :/ I would rather splt this task
into two:

 - make stack 1M by default and madvise as not needed and merge,
   it upstream asap, to not block users

 - second series is to optimize stack usage

> > 
> > This won't work. Imagine we put wmark in _first_ page, and then we find
> > that the wmark has been overwriten, where to put next mark then? Or
> > you propose to catch signals?
> 
> Put the next watermark in the second page then. If it gets overwritten,
> too, put it in the third page, and so on. Perhaps, we can even double
> the minimal stack allocation each time.

ok

> > > 
> > > Why not rand?
> > 
> > Because we already have a helper for random numbers :)
> 
> It's a helper for filling an array with random bytes. I don't see much
> point in using it for generating a single random number.

ok

	Cyrill