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

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Message-ID: <20250908141423.GJ616306@nvidia.com>
Date: Mon, 8 Sep 2025 11:14:23 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Graf <graf@...zon.com>, Baoquan He <bhe@...hat.com>,
	Changyuan Lyu <changyuanl@...gle.com>, Chris Li <chrisl@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Pratyush Yadav <pratyush@...nel.org>, kexec@...ts.infradead.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] kho: add support for preserving vmalloc
 allocations

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