Date:   Tue, 10 Dec 2019 19:45:28 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "linyunsheng@...wei.com" <linyunsheng@...wei.com>,
        "brouer@...hat.com" <brouer@...hat.com>
CC:     "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        Li Rongqing <lirongqing@...du.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH][v2] page_pool: handle page recycle for NUMA_NO_NODE
 condition

On Tue, 2019-12-10 at 09:31 +0800, Yunsheng Lin wrote:
> On 2019/12/10 7:34, Saeed Mahameed wrote:
> > On Mon, 2019-12-09 at 13:14 +0100, Jesper Dangaard Brouer wrote:
> > > On Sat, 7 Dec 2019 03:52:41 +0000
> > > Saeed Mahameed <saeedm@...lanox.com> wrote:
> > > 
> > > > On Fri, 2019-12-06 at 17:32 +0800, Li RongQing wrote:
> > > > > some drivers uses page pool, but not require to allocate
> > > > > pages from bound node, or simply assign pool.p.nid to
> > > > > NUMA_NO_NODE, and the commit d5394610b1ba ("page_pool:
> > > > > Don't recycle non-reusable pages") will block this kind
> > > > > of driver to recycle
> > > > > 
> > > > > so take page as reusable when page belongs to current
> > > > > memory node if nid is NUMA_NO_NODE
> > > > > 
> > > > > v1-->v2: add check with numa_mem_id from Yunsheng
> > > > > 
> > > > > Fixes: d5394610b1ba ("page_pool: Don't recycle non-reusable
> > > > > pages")
> > > > > Signed-off-by: Li RongQing <lirongqing@...du.com>
> > > > > Suggested-by: Yunsheng Lin <linyunsheng@...wei.com>
> > > > > Cc: Saeed Mahameed <saeedm@...lanox.com>
> > > > > ---
> > > > >  net/core/page_pool.c | 7 ++++++-
> > > > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > > > > index a6aefe989043..3c8b51ccd1c1 100644
> > > > > --- a/net/core/page_pool.c
> > > > > +++ b/net/core/page_pool.c
> > > > > @@ -312,12 +312,17 @@ static bool
> > > > > __page_pool_recycle_direct(struct
> > > > > page *page,
> > > > >  /* page is NOT reusable when:
> > > > >   * 1) allocated when system is under some pressure.
> > > > > (page_is_pfmemalloc)
> > > > >   * 2) belongs to a different NUMA node than pool->p.nid.
> > > > > + * 3) belongs to a different memory node than current
> > > > > context
> > > > > + * if pool->p.nid is NUMA_NO_NODE
> > > > >   *
> > > > >   * To update pool->p.nid users must call
> > > > > page_pool_update_nid.
> > > > >   */
> > > > >  static bool pool_page_reusable(struct page_pool *pool,
> > > > > struct
> > > > > page
> > > > > *page)
> > > > >  {
> > > > > -	return !page_is_pfmemalloc(page) && page_to_nid(page)
> > > > > ==
> > > > > pool-  
> > > > > > p.nid;  
> > > > > +	return !page_is_pfmemalloc(page) &&
> > > > > +		(page_to_nid(page) == pool->p.nid ||
> > > > > +		(pool->p.nid == NUMA_NO_NODE &&
> > > > > +		page_to_nid(page) == numa_mem_id()));
> > > > >  }
> > > > >    
> > > > 
> > > > Cc'ed Jesper, Ilias & Jonathan.
> > > > 
> > > > I don't think it is correct to check that the page nid is same
> > > > as
> > > > numa_mem_id() if pool is NUMA_NO_NODE. In such case we should
> > > > allow
> > > > all
> > > > pages to recycle, because you can't assume where pages are
> > > > allocated
> > > > from and where they are being handled.
> > > > 
> > > > I suggest the following:
> > > > 
> > > > return !page_pfmemalloc() && 
> > > > ( page_to_nid(page) == pool->p.nid || pool->p.nid ==
> > > > NUMA_NO_NODE
> > > > );
> > > > 
> > > > 1) never recycle emergency pages, regardless of pool nid.
> > > > 2) always recycle if pool is NUMA_NO_NODE.
> > > > 
> > > > the above change should not add any overhead, a modest branch
> > > > predictor
> > > > will handle this with no effort.
> > > > 
> > > > Jesper et al. what do you think?
> > > 
> > > The patch description doesn't explain the problem very well.
> > > 
> > > Lets first establish what the problem is.  After I took at closer
> > > look,
> > > I do think we have a real problem here...
> > > 
> > > If function alloc_pages_node() is called with NUMA_NO_NODE (see
> > > below
> > > signature), then the nid is re-assigned to numa_mem_id().
> > > 
> > > Our current code checks: page_to_nid(page) == pool->p.nid which
> > > seems
> > > bogus, as pool->p.nid=NUMA_NO_NODE and the page NID will not
> > > return
> > > NUMA_NO_NODE... as it was set to the local detect numa node,
> > > right?
> > > 
> > 
> > right.
> > 
> > > So, we do need a fix... but the question is that semantics do we
> > > want?
> > > 
> > 
> > maybe assume that __page_pool_recycle_direct() is always called
> > from
> > the right node and change the current bogus check:
> > 
> > from:
> > page_to_nid(page) == pool->p.nid 
> > 
> > to:
> > page_to_nid(page) == numa_mem_id()
> > 
> > This will allow recycling only if handling node is the same as
> > where
> > the page was allocated, regardless of pool->p.nid.
> > 
> > so semantics are:
> > 
> > 1) allocate from: pool->p.nid, as chosen by user.
> > 2) recycle when: page_to_nid(page) == numa_mem_id().
> > 3) pool user must guarantee that the handler will run on the right
> > node. which should always be the case. otherwise recycling will be
> > skipped (no cross numa recycling).
> > 
> > 
> > a) if the pool migrates, we will stop recycling until the pool
> > moves
> > back to original node, or user calls pool_update_nid() as we do in
> > mlx5.
> > b) if pool is NUMA_NO_NODE, then allocation and handling will be
> > done
> > on numa_mem_id(), which means the above check will work.
> 
> Only checking page_to_nid(page) == numa_mem_id() may not work for the
> below
> case in mvneta.c:
> 
> static int mvneta_create_page_pool(struct mvneta_port *pp,
> 				   struct mvneta_rx_queue *rxq, int
> size)
> {
> 	struct bpf_prog *xdp_prog = READ_ONCE(pp->xdp_prog);
> 	struct page_pool_params pp_params = {
> 		.order = 0,
> 		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
> 		.pool_size = size,
> 		.nid = cpu_to_node(0),
> 		.dev = pp->dev->dev.parent,
> 		.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL :
> DMA_FROM_DEVICE,
> 		.offset = pp->rx_offset_correction,
> 		.max_len = MVNETA_MAX_RX_BUF_SIZE,
> 	};
> 
> the pool->p.nid is not NUMA_NO_NODE, then the node of page allocated
> for rx
> may not be numa_mem_id() when running in the NAPI polling, because
> pool->p.nid
> is not the same as the node of cpu running in the NAPI polling.
> 
> Does the page pool support recycling for above case?
> 

I don't think you want to allow cross numa recycling.

> Or we "fix' the above case by setting pool->p.nid to
> NUMA_NO_NODE/dev_to_node(),
> or by calling pool_update_nid() in NAPI polling as mlx5 does?
> 

Yes just update_nid when needed, and make sure the NAPI polling runs on
a consistent core and eventually alloc/recycling will happen on the
same core.

> 
> > Thanks,
> > Saeed.
> > 
> > 
> > 
> > 
> > 
> > 
> > 

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