Re: [PATCH v5] mm/alloc_tag: replace fixed-size early PFN array with dynamic linked list

Re: [PATCH v5] mm/alloc_tag: replace fixed-size early PFN array with dynamic linked list

[Andrew Morton]

On Wed,  6 May 2026 10:22:56 +0800 Hao Ge <hao.ge@linux.dev> wrote:

> Pages allocated before page_ext is available have their codetag left
> uninitialized. Track these early PFNs and clear their codetag in
> clear_early_alloc_pfn_tag_refs() to avoid "alloc_tag was not set"
> warnings when they are freed later.
> 
> Currently a fixed-size array of 8192 entries is used, with a warning if
> the limit is exceeded. However, the number of early allocations depends
> on the number of CPUs and can be larger than 8192.
> 
> Replace the fixed-size array with a dynamically allocated linked list
> of pfn_pool structs. Each node is allocated via alloc_page() and mapped
> to a pfn_pool containing a next pointer, an atomic slot counter, and a
> PFN array that fills the remainder of the page.
> 
> The tracking pages themselves are allocated via alloc_page(), which
> would trigger __pgalloc_tag_add() -> alloc_tag_add_early_pfn() and
> recurse indefinitely. Introduce __GFP_NO_CODETAG (reuses the
> %__GFP_NO_OBJ_EXT bit) and pass gfp_flags through pgalloc_tag_add()
> so that the early path can skip recording allocations that carry this
> flag.

AI review asked a couple of things.  I have a feeling we saw at least
one of these, so probably already dealt with.
	https://sashiko.dev/#/patchset/20260506022256.32664-1-hao.ge@linux.dev