On Mon, 04 May 2015 16:14:48 -0700 Alexander Duyck <alexander.h.duyck@xxxxxxxxxx> wrote:
> +/**
> + * skb_free_frag - free a page fragment
> + * @head: virtual address of page fragment
> + *
> + * Frees a page fragment allocated out of either a compound or order 0 page.
> + * The function itself is a hybrid between free_pages and free_compound_page
> + * which can be found in mm/page_alloc.c
> + */
> +void skb_free_frag(void *head)
> +{
> + struct page *page = virt_to_head_page(head);
> +
> + if (unlikely(put_page_testzero(page))) {
> + if (likely(PageHead(page)))
> + __free_pages_ok(page, compound_order(page));
> + else
> + free_hot_cold_page(page, false);
> + }
> +}
Why are we testing for PageHead in here? If the code were to simply do
if (unlikely(put_page_testzero(page)))
__free_pages_ok(page, compound_order(page));
that would still work?
There's nothing networking-specific in here. I suggest the function be
renamed and moved to page_alloc.c. Add an inlined skb_free_frag() in a
net header which calls it. This way the mm developers know about it
and will hopefully maintain it. It would need a comment explaining
when and why people should and shouldn't use it.
The term "page fragment" is a net thing and isn't something we know
about. What is it? From context I'm thinking a definition would look
something like
An arbitrary-length arbitrary-offset area of memory which resides
within a 0 or higher order page. Multiple fragments within that page
are individually refcounted, in the page's reference counter.
Is that correct and complete?
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