Re: Request for clarification regarding huge pages and remapping of virtual to physical address

[David Hildenbrand <david@redhat.com>]

On 17.04.24 11:11, sunil bhargo wrote:
> Hi,
> 
> We have an application which relies on virtual address to physical 
> address mapping to remain static. The buffer is allocated using 
> malloc. It is in user space and we were using the mlock thinking that as 
> it would prevent the swapping the va->pa address mapping would be 
> static. But it seems to be a faulty assumption.
> 
> If the memory is allocated from huge pages by reserving space upfront at 
> the kernel boot up and then mmap’ing using MAP_HUGETLB, is it assured 
> that virtual address to physical mapping won’t be remapped and will be 
> static ?

Unless you have a kernel that has page migration disabled, no.

You could use secretmem (which is currently not migratabale/swappable/ 
...), but that has very limited capabilities.

A "hack" would be to register that (ordinary) memory using iouring as a 
fixed buffer. That way, it will be longterm pinned and can neither get 
migrated nor swapped out.

-- 
Cheers,

David / dhildenb