On Mon, Sep 01, 2025 at 07:02:46PM +0000, Pasha Tatashin wrote:

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This really wants some luo helper

'luo alloc array'
'luo restore array'
'luo free array'

We can just add kho_{preserve,restore}_vmalloc(). I've drafted it here:
https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kho/vmalloc/v1

The patch looks okay to me, but it doesn't support holes in vmap
areas. While that is likely acceptable for vmalloc, it could be a
problem if we want to preserve memfd with holes and using vmap
preservation as a method, which would require a different approach.
Still, this would help with preserving memfd.

I agree. I think we should do it the other way round. Build a sparse
array first, and then use that to build vmap preservation. Our emails

Yes, sparse array support would help both: vmalloc and memfd preservation.

Why? vmalloc is always full popoulated, no sparseness..

And again in real systems we expect memfd to be fully populated too.

I wouldn't invest any time in something like this right now. Just be
inefficient if there is sparseness for some reason.

Jason