Re: Summary of LSF-MM Volatile Ranges Discussion

[John Stultz <john.stultz@linaro.org>]

On 04/22/2013 11:51 PM, Dmitry Vyukov wrote:
> Just want to make sure our case does not fall out of the discussion:
> https://code.google.com/p/thread-sanitizer/wiki/VolatileRanges

Yes, while I forgot to mention it in the summary, I did bring it up 
briefly, but I cannot claim to have done it justice.

Personally, while I suspect we might be able to support your desired 
semantics (ie: mark once volatile, always zero-fill, no sigbus) via a 
mode flag

> While reading your email, I remembered that we actually have some
> pages mapped from a file inside the range. So it's like 70TB of ANON
> mapping + few pages in the middle mapped from FILE. The file is mapped
> with MAP_PRIVATE + PROT_READ, it's read-only and not shared.
> But we want to mark the volatile range only once on startup, so
> performance is not a serious concern (while the function in executed
> in say no more than 10ms).
> If the mixed ANON+FILE ranges becomes a serious problem, we are ready
> to remove FILE mappings, because it's only an optimization. I.e. we
> can make it pure ANON mapping.
Well, in my mind, the MAP_PRIVATE mappings are semantically the same as 
anonymous memory with regards to volatility. So I hope this wouldn't be 
an issue.

thanks
-john

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