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

From: Mel Gorman <[email-masked]>
Date: Sat, 13 Mar 2021 13:30:58 +0000

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