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Date: Thu, 22 May 2025 22:19:56 +0000
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Subject: Re: [RFC PATCH v2 38/51] KVM: guest_memfd: Split allocator pages for
 guest_memfd use

On Wed, 2025-05-14 at 16:42 -0700, Ackerley Tng wrote:
> +
> +static pgoff_t kvm_gmem_compute_invalidate_bound(struct inode *inode,
> +						 pgoff_t bound, bool start)
> +{
> +	size_t nr_pages;
> +	void *priv;
> +
> +	if (!kvm_gmem_has_custom_allocator(inode))

General comment - It's a bit unfortunate how kvm_gmem_has_custom_allocator() is
checked all over the place across this series. There are only two allocators
after this, right? So one is implemented with callbacks presumably designed to
fit other allocators, and one has special case logic in guest_memfd.c.

Did you consider designing struct guestmem_allocator_operations so that it could
encapsulate the special logic for both the existing and new allocators? If it
didn't work well, could we expect that a next allocator would actually fit
struct guestmem_allocator_operations?

> +		return bound;
> +
> +	priv = kvm_gmem_allocator_private(inode);
> +	nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(priv);
> +
> +	if (start)
> +		return round_down(bound, nr_pages);
> +	else
> +		return round_up(bound, nr_pages);
> +}
> +
> +static pgoff_t kvm_gmem_compute_invalidate_start(struct inode *inode,
> +						 pgoff_t bound)
> +{
> +	return kvm_gmem_compute_invalidate_bound(inode, bound, true);
> +}
> +
> +static pgoff_t kvm_gmem_compute_invalidate_end(struct inode *inode,
> +					       pgoff_t bound)
> +{
> +	return kvm_gmem_compute_invalidate_bound(inode, bound, false);
> +}
> +

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