netdev - Re: [PATCH][v2] page_pool: handle page recycle for NUMA_NO

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Date:   Sat, 7 Dec 2019 03:52:41 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "linyunsheng@...wei.com" <linyunsheng@...wei.com>,
        Li Rongqing <lirongqing@...du.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>
Subject: Re: [PATCH][v2] page_pool: handle page recycle for NUMA_NO_NODE
 condition

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?

-Saeed.