From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 26 Feb 2019 15:34:56 +0300 From: Vladimir Davydov Subject: Re: [RFC v3] fiber: Increase default stack size Message-ID: <20190226123456.k66j25qv57vygm6u@esperanza> References: <20190222201639.GA7198@uranus> <20190225145516.6fdmob3tdkft5sky@esperanza> <20190225213955.GI7198@uranus> <20190226085852.ugkqo6dz5nmjbhze@esperanza> <20190226091254.GL7198@uranus> <20190226102656.gwwy35jyaqdkci3l@esperanza> <20190226111632.GM7198@uranus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190226111632.GM7198@uranus> To: Cyrill Gorcunov Cc: =?utf-8?B?0JPQtdC+0YDQs9C40Lkg0JrQuNGA0LjRh9C10L3QutC+?= , tarantool-patches@freelists.org List-ID: On Tue, Feb 26, 2019 at 02:16:32PM +0300, Cyrill Gorcunov wrote: > > - 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. Yeah, good point, I haven't thought about it. Then we have to either always allocate a big stack for the main fiber or use an environment variable. Let's get back to it later and first make the stack size limit statically defined. > > > - 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. Hmm, why? Consider the example with PATH_MAX buffer. Putting dirty marks at page boundaries doesn't guarantee any of them will get overwritten by the buffer if only a few hundred of bytes are used. I think we should dirty the last page or two at random intervals - this should increase the chance that at least one mark is overwritten by any function that is eager for the stack.