Re: [PATCH v3 1/2] kho: add support for preserving vmalloc allocations

Jason Gunthorpe
2025-09-08T14:14:29Z

On Mon, Sep 08, 2025 at 01:35:27PM +0300, Mike Rapoport wrote:
> +static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)
> +{
> + struct kho_vmalloc_chunk *chunk;
> + int err;
> +
> + chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
> + if (!chunk)
> + return NULL;
> +
> + err = kho_preserve_phys(virt_to_phys(chunk), PAGE_SIZE);
> + if (err)
> + goto err_free;

kzalloc() cannot be preserved, the only thing we support today is
alloc_page(), so this code pattern shouldn't exist.

Call alloc_page() and use a kho_preserve_page/folio() like the luo
patches were doing. The pattern seems common it probably needs a small
alloc/free helper.

> + for (int i = 0; i < vm->nr_pages; i += (1 << order)) {
> + phys_addr_t phys = page_to_phys(vm->pages[i]);
> +
> + err = __kho_preserve_order(track, PHYS_PFN(phys), order);
> + if (err)
> + goto err_free;

I think you should make a helper inline to document what is happening here:

/*
* Preserve a contiguous aligned list of order 0 pages that aggregate
* to a higher order allocation. Must be restored using
* kho_restore_page() on each order 0 page.
*/
kho_preserve_pages(page, order);

Jason