netdev - Re: [PATCH net-next v8 2/4] page_pool: halve BIAS_MAX for multiple user references of a fragment

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Date: Mon, 11 Dec 2023 11:12:01 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: netdev@...r.kernel.org, linux-mm@...ck.org, kuba@...nel.org,
 ilias.apalodimas@...aro.org, jasowang@...hat.com, linyunsheng@...wei.com,
 Liang Chen <liangchen.linux@...il.com>, edumazet@...gle.com,
 davem@...emloft.net, almasrymina@...gle.com, pabeni@...hat.com
Subject: Re: [PATCH net-next v8 2/4] page_pool: halve BIAS_MAX for multiple
 user references of a fragment

Hi Alex,

For page_pool BIAS stuff I would really appreciate your review please.
-Jesper


On 11/12/2023 04.52, Liang Chen wrote:
> Referring to patch [1], in order to support multiple users referencing the
> same fragment and prevent overflow from pp_ref_count growing, the initial
> value of pp_ref_count is halved, leaving room for pp_ref_count to increment
> before the page is drained.
> 
> [1]
> https://lore.kernel.org/all/20211009093724.10539-3-linyunsheng@huawei.com/
> 
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> Reviewed-by: Yunsheng Lin <linyunsheng@...wei.com>
> ---
>   net/core/page_pool.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 106220b1f89c..436f7ffea7b4 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -26,7 +26,7 @@
>   #define DEFER_TIME (msecs_to_jiffies(1000))
>   #define DEFER_WARN_INTERVAL (60 * HZ)
>   
> -#define BIAS_MAX	LONG_MAX
> +#define BIAS_MAX	(LONG_MAX >> 1)
>   
>   #ifdef CONFIG_PAGE_POOL_STATS
>   /* alloc_stat_inc is intended to be used in softirq context */