Re: [PATCH v6 3/4] iommu: debug-pagealloc: Track IOMMU pages
From: David Hildenbrand (Red Hat)
Date: Mon Jan 12 2026 - 14:12:00 EST
On 1/12/26 15:58, Mostafa Saleh wrote:
On Mon, Jan 12, 2026 at 1:52 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
On Mon, Jan 12, 2026 at 01:43:41PM +0000, Mostafa Saleh wrote:
But I don’t see why not. from the documentation:
/**
* pfn_valid - check if there is a valid memory map entry for a PFN
* @pfn: the page frame number to check
*
* Check if there is a valid memory map entry aka struct page for the @pfn.
* Note, that availability of the memory map entry does not imply that
* there is actual usable memory at that @pfn. The struct page may
* represent a hole or an unusable page frame.
…
That means that struct page exists, which is all what we need here.
A struct page that has never been initialize shouldn't ever be read. I
don't know how that relates to page_ext, but are you really sure that
is all you need?
AFAIU, if pfn_valid() returns true, it means the struct page is valid,
and lookup_page_ext() will check that a valid page_ext exists for this
entry.
Not always. Offline memory blocks have a memory map but no page ext. We allocate the page ext at memory onlining time.
Also, I'm not sure about ZONE_DEVICE memory, very likely we never allocate a page_ext for them?
I'd assume both cases are not relevant for your use case, though.
--
Cheers
David