Re: [PATCH v5 00/11] Virtual Swap Space (Swap Table Edition)

[Nhat Pham]

On Fri, Sep 18, 2026 at 11:02 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> Patch 11 is an RFC. It swaps vswap's cluster xarray for the VM_SPARSE
> vmalloc array Baoquan He designed for xswap, to show that the data
> structure and the device model are separable: moving to his is one
> self-contained patch that adds no userspace interface. Note that
> per Baoquan's commentary (see [5]), I have skipped shrink for now, only
> freeing vtable when the cluster becomes free to minimize metadata
> overhead while keeping the skeleton in the free list. I have not done
> performance testing on this patch yet (the number is from the old design),
> but I have run a suite of simple stress tests.
>
> It is adapted almost entirely from Baoquan's code (see [6]), so I have
> kept Baoquan's Co-developed-by and Signed-off-by tag.

To clarify a bit on the motivation of this exercise: Kairui and
Baoquan raised the concerns (for e.g in [1]) that if we were to go
with the xarray as a data structure first, switching it to the
VM_SPARSE vmalloc array would be difficult. I want to check this claim
by prototyping such a conversion. It is fairly straightforward and
simple to me. So it is not a valid concern to block the landing of
vswap.

If we are to actually switch to such a data structure, Baoquan should
be the one driving this, by showing that there are performance wins to
the switch :) It is his proposal, so the onus is on him to drive it to
completion. I'm happy to assist with the reviewing and testing!

[1]: https://lore.kernel.org/all/CAMgjq7AHRzBsbmGOx0s=TQFBwcn=DEU1naR443sO6x+pJd6hAg@xxxxxxxxxxxxxx/