Re: Rationale for RLIMIT_MEMLOCK?

[Arjan van de Ven]

> c() was the function in question.
> 
> JÃrg, if we're talking about valloc(), this hasn't much to do with the
> kernel, but is a library issue.
> 
> There is _no_ documentation that says valloc() or memalign() or
> posix_memalign() is required to use mmap(). It works on some systems and
> for some allocation sizes as a side effect of the valloc()
> implementation.

it doesn't matter. Regardless of the method, the memory has to be locked
due to the FUTURE requirement.



> And because this requirement is not specified in the relevant standards,
> it is wrong to assume valloc() returns locked pages. 

is it? I sort of doubt that (but I'm not a standards expert, but I'd
expect that "lock all in the future" applies to all memory, not just
mmap'd memory

> You cannot rely on
> mmap() returning locked pages after mlockall() either, because you might
> be exceeding resource limits.

this is true and fully correct



the situation is messy; I can see some value in the hack Ted proposed to
just bump the rlimit automatically at an mlockall-done-by-root.. but to
be fair it's a hack :(


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/