Travis Downs (travis.downs.delete@this.gmail.com) on June 5, 2019 4:48 pm wrote:
> On Linux, given a mapped-but-probably-not-populated anonymous region
> of memory, is there any way to ask the kernel to populate it?

> The usual approach is just to write to it, but on x86 you take a fault for every 4k page - and
> thanks to our friends Spectre and Meltdown this hurts a lot more than it used to. I know I'm about
> to write to all this memory, so I'd like to just populate the entire region right now.

> If I were allocating the memory myself with mmap, the solution is just to pass MAP_POPULATE
> to mmap. However, there are scenarios were I'm not allocating the memory, can I can't control
> the caller, but I'd like to populate all the pages after the initial allocation.

> One dirty hack is back-to-back mlock()/munlock() on the region, but this does way more work than
> is necessary (all the munlock() is wasted, and anything mlock() does other than filling the PTEs
> is wasted as well). Moreover, it isn't work for non-privledged processes unless you restrict the
> granularity to RLIMIT_MEMLOCK, and on memory constrained systems you might blow yourself up.

Just MAP_FIXED|MAP_POPULATE over page rages not mincore()? You're at least safe from mlock() ulimits then.