netdev - Re: [PATCH RFC net-next 2/3] net: page_pool: use alloc_pages

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Date:   Fri, 26 Feb 2021 15:31:49 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>, linux-mm@...ck.org,
        chuck.lever@...cle.com, netdev@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        brouer@...hat.com
Subject: Re: [PATCH RFC net-next 2/3] net: page_pool: use alloc_pages_bulk
 in refill code path

On Wed, 24 Feb 2021 22:15:22 +0200
Ilias Apalodimas <ilias.apalodimas@...aro.org> wrote:

> Hi Jesper, 
> 
> On Wed, Feb 24, 2021 at 07:56:46PM +0100, Jesper Dangaard Brouer wrote:
> > There are cases where the page_pool need to refill with pages from the
> > page allocator. Some workloads cause the page_pool to release pages
> > instead of recycling these pages.
> > 
> > For these workload it can improve performance to bulk alloc pages from
> > the page-allocator to refill the alloc cache.
> > 
> > For XDP-redirect workload with 100G mlx5 driver (that use page_pool)
> > redirecting xdp_frame packets into a veth, that does XDP_PASS to create
> > an SKB from the xdp_frame, which then cannot return the page to the
> > page_pool. In this case, we saw[1] an improvement of 18.8% from using
> > the alloc_pages_bulk API (3,677,958 pps -> 4,368,926 pps).
> > 
> > [1] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org
> > 
> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>  
> 
> [...]
> 
> > +	/* Remaining pages store in alloc.cache */
> > +	list_for_each_entry_safe(page, next, &page_list, lru) {
> > +		list_del(&page->lru);
> > +		if (pp_flags & PP_FLAG_DMA_MAP) {
> > +			page = page_pool_dma_map(pool, page);
> > +			if (!page)  
> 
> As I commented on the previous patch, i'd prefer the put_page() here to be
> explicitly called, instead of hiding in the page_pool_dma_map()

I fully agree.  I will fixup the code.

> > +				continue;
> > +		}
> > +		if (likely(pool->alloc.count < PP_ALLOC_CACHE_SIZE)) {
> > +			pool->alloc.cache[pool->alloc.count++] = page;
> > +			pool->pages_state_hold_cnt++;
> > +			trace_page_pool_state_hold(pool, page,
> > +						   pool->pages_state_hold_cnt);
> > +		} else {
> > +			put_page(page);
> > +		}
> > +	}
> > +out:
> >  	if (pool->p.flags & PP_FLAG_DMA_MAP) {
> > -		page = page_pool_dma_map(pool, page);
> > -		if (!page)
> > +		first_page = page_pool_dma_map(pool, first_page);
> > +		if (!first_page)
> >  			return NULL;
> >  	}
> >    
> [...]

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer