On Fri, Jun 16, 2023 at 05:12:44PM +0100, David Howells wrote:

...

+/**
+ * alloc_skb_frag - Allocate a page fragment for using in a socket
+ * @fragsz: The size of fragment required
+ * @gfp: Allocation flags
+ */
+void *alloc_skb_frag(size_t fragsz, gfp_t gfp)
+{
+	struct skb_splice_frag_cache *cache;
+	struct folio *folio, *spare = NULL;
+	size_t offset, fsize;
+	void *p;
+
+	if (WARN_ON_ONCE(fragsz == 0))
+		fragsz = 1;
+
+	cache = get_cpu_ptr(&skb_splice_frag_cache);
+reload:
+	folio = cache->folio;
+	offset = cache->offset;
+try_again:
+	if (fragsz > offset)
+		goto insufficient_space;
+
+	/* Make the allocation. */
+	cache->pagecnt_bias--;
+	offset = ALIGN_DOWN(offset - fragsz, SMP_CACHE_BYTES);
+	cache->offset = offset;
+	p = cache->virt + offset;
+	put_cpu_ptr(skb_splice_frag_cache);

Hi David,

I don't think it makes any difference at run-time.
But to keep Sparse happy, perhaps this ought to be put_cpu_var()

...