linux-kernel - Re: [PATCH 7/7] net: page_pool: use alloc_pages

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Message-ID: <20210313133058.GZ3697@techsingularity.net>
Date:   Sat, 13 Mar 2021 13:30:58 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Net <netdev@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-NFS <linux-nfs@...r.kernel.org>
Subject: 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:
> > -       /* 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