I like the explanation.
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
> On Oct 26, 2020, at 8:55 PM, Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> wrote:
>
> Provide some guidance towards when this might not be the right interface
> to use.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/page_alloc.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 23f5066bd4a5..e613177b8041 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5007,6 +5007,26 @@ static inline void free_the_page(struct page *page, unsigned int order)
> __free_pages_ok(page, order, FPI_NONE);
> }
>
> +/**
> + * __free_pages - Free pages allocated with alloc_pages().
> + * @page: The page pointer returned from alloc_pages().
> + * @order: The order of the allocation.
> + *
> + * This function can free multi-page allocations that are not compound
> + * pages. It does not check that the @order passed in matches that of
> + * the allocation, so it is easy to leak memory. Freeing more memory
> + * than was allocated will probably emit a warning.
> + *
> + * If the last reference to this page is speculative, it will be released
> + * by put_page() which only frees the first page of a non-compound
> + * allocation. To prevent the remaining pages from being leaked, we free
> + * the subsequent pages here. If you want to use the page's reference
> + * count to decide when to free the allocation, you should allocate a
> + * compound page, and use put_page() instead of __free_pages().
> + *
> + * Context: May be called in interrupt context or while holding a normal
> + * spinlock, but not in NMI context or while holding a raw spinlock.
> + */
> void __free_pages(struct page *page, unsigned int order)
> {
> if (put_page_testzero(page))
> --
> 2.28.0
>
>
