Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path

On Fri, Mar 12, 2021 at 11:44:09AM -0800, Alexander Duyck wrote:

quoted

-       /* FUTURE development:
-        *
-        * Current slow-path essentially falls back to single page
-        * allocations, which doesn't improve performance.  This code
-        * need bulk allocation support from the page allocator code.
-        */
-
-       /* Cache was empty, do real allocation */
-#ifdef CONFIG_NUMA
-       page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
-#else
-       page = alloc_pages(gfp, pool->p.order);
-#endif
-       if (!page)
+       if (unlikely(!__alloc_pages_bulk(gfp, pp_nid, NULL, bulk, &page_list)))
                return NULL;

+       /* First page is extracted and returned to caller */
+       first_page = list_first_entry(&page_list, struct page, lru);
+       list_del(&first_page->lru);
+

This seems kind of broken to me. If you pull the first page and then
cannot map it you end up returning NULL even if you placed a number of
pages in the cache.

I think you're right but I'm punting this to Jesper to fix. He's more
familiar with this particular code and can verify the performance is
still ok for high speed networks.

-- 
Mel Gorman
SUSE Labs