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From: Jesper Dangaard Brouer <jbrouer@redhat.com>
To: Yunsheng Lin <linyunsheng@huawei.com>,
	davem@davemloft.net, kuba@kernel.org
Cc: brouer@redhat.com, alexander.duyck@gmail.com,
	linux@armlinux.org.uk, mw@semihalf.com, linuxarm@openeuler.org,
	yisen.zhuang@huawei.com, salil.mehta@huawei.com,
	thomas.petazzoni@bootlin.com, hawk@kernel.org,
	ilias.apalodimas@linaro.org, ast@kernel.org,
	daniel@iogearbox.net, john.fastabend@gmail.com,
	akpm@linux-foundation.org, peterz@infradead.org, will@kernel.org,
	willy@infradead.org, vbabka@suse.cz, fenghua.yu@intel.com,
	guro@fb.com, peterx@redhat.com, feng.tang@intel.com,
	jgg@ziepe.ca, mcroce@microsoft.com, hughd@google.com,
	jonathan.lemon@gmail.com, alobakin@pm.me, willemb@google.com,
	wenxu@ucloud.cn, cong.wang@bytedance.com, haokexin@gmail.com,
	nogikh@google.com, elver@google.com, yhs@fb.com,
	kpsingh@kernel.org, andrii@kernel.org, kafai@fb.com,
	songliubraving@fb.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	chenhao288@hisilicon.com
Subject: Re: [PATCH net-next v2 2/4] page_pool: add interface to manipulate frag count in page pool
Date: Thu, 12 Aug 2021 17:17:05 +0200	[thread overview]
Message-ID: <d9bce937-1645-b209-a1d4-c7c0a6fcd1af@redhat.com> (raw)
In-Reply-To: <1628217982-53533-3-git-send-email-linyunsheng@huawei.com>


On 06/08/2021 04.46, Yunsheng Lin wrote:
> +static inline long page_pool_atomic_sub_frag_count_return(struct page *page,
> +							  long nr)
> +{
> +	long ret;
> +
> +	/* As suggested by Alexander, atomic_long_read() may cover up the
> +	 * reference count errors, so avoid calling atomic_long_read() in
> +	 * the cases of freeing or draining the page_frags, where we would
> +	 * not expect it to match or that are slowpath anyway.
> +	 */
> +	if (__builtin_constant_p(nr) &&
> +	    atomic_long_read(&page->pp_frag_count) == nr)
> +		return 0;
> +
> +	ret = atomic_long_sub_return(nr, &page->pp_frag_count);
> +	WARN_ON(ret < 0);

I worried about this WARN_ON() as it generates an 'ud2' instruction 
which influence I-cache fetching.  But I have disassembled (objdump) the 
page_pool.o binary and the ud2 gets placed last in the main function 
page_pool_put_page() that use this inlined function.
Thus, I assume this is not a problem :-)


> +	return ret;


  parent reply	other threads:[~2021-08-12 15:17 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-06  2:46 [PATCH net-next v2 0/4] add frag page support " Yunsheng Lin
2021-08-06  2:46 ` [PATCH net-next v2 1/4] page_pool: keep pp info as long as page pool owns the page Yunsheng Lin
2021-08-06  2:46 ` [PATCH net-next v2 2/4] page_pool: add interface to manipulate frag count in page pool Yunsheng Lin
2021-08-10 14:58   ` Jesper Dangaard Brouer
2021-08-11  0:48     ` Yunsheng Lin
2021-08-12 15:17   ` Jesper Dangaard Brouer [this message]
2021-08-06  2:46 ` [PATCH net-next v2 3/4] page_pool: add frag page recycling support " Yunsheng Lin
2021-08-06  2:46 ` [PATCH net-next v2 4/4] net: hns3: support skb's frag page recycling based on " Yunsheng Lin
2021-09-08  8:31   ` moyufeng
2021-09-08 15:08     ` Jakub Kicinski
2021-09-08 15:26       ` Ilias Apalodimas
2021-09-08 15:57         ` Jakub Kicinski
2021-09-08 16:47           ` Jesper Dangaard Brouer
2021-09-08 16:51           ` Ilias Apalodimas
2022-01-26 14:30   ` Jean-Philippe Brucker
2022-01-28  4:00     ` Yunsheng Lin
2022-01-28  9:21       ` Jean-Philippe Brucker
2022-01-29  8:44         ` Yunsheng Lin
2022-02-03  9:48           ` Jean-Philippe Brucker
2022-02-07  2:54             ` Yunsheng Lin
2022-03-24 18:09               ` Jean-Philippe Brucker
2021-08-10 14:01 ` [PATCH net-next v2 0/4] add frag page support in " Jakub Kicinski
2021-08-10 14:23   ` Jesper Dangaard Brouer
2021-08-10 14:43     ` Jakub Kicinski
2021-08-10 15:09       ` Alexander Duyck
2021-08-11  1:06         ` [Linuxarm] " Yunsheng Lin

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