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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Marcin Wojtas <mw@semihalf.com>,
	linuxarm@openeuler.org, yisen.zhuang@huawei.com,
	Salil Mehta <salil.mehta@huawei.com>,
	thomas.petazzoni@bootlin.com, hawk@kernel.org,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	fenghua.yu@intel.com, guro@fb.com, Peter Xu <peterx@redhat.com>,
	Feng Tang <feng.tang@intel.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	Matteo Croce <mcroce@microsoft.com>,
	Hugh Dickins <hughd@google.com>,
	Jonathan Lemon <jonathan.lemon@gmail.com>,
	Alexander Lobakin <alobakin@pm.me>,
	Willem de Bruijn <willemb@google.com>,
	wenxu@ucloud.cn, Cong Wang <cong.wang@bytedance.com>,
	Kevin Hao <haokexin@gmail.com>,
	nogikh@google.com, Marco Elver <elver@google.com>,
	Yonghong Song <yhs@fb.com>,
	kpsingh@kernel.org, andrii@kernel.org,
	Martin KaFai Lau <kafai@fb.com>,
	songliubraving@fb.com, Netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH rfc v6 2/4] page_pool: add interface to manipulate frag count in page pool
Date: Tue, 20 Jul 2021 08:43:42 -0700	[thread overview]
Message-ID: <CAKgT0Uf=WbpngDPQ1V0X+XSJbZ91=cuaz8r_J96=BrXg01PJFA@mail.gmail.com> (raw)
In-Reply-To: <1626752145-27266-3-git-send-email-linyunsheng@huawei.com>

On Mon, Jul 19, 2021 at 8:36 PM Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> For 32 bit systems with 64 bit dma, dma_addr[1] is used to
> store the upper 32 bit dma addr, those system should be rare
> those days.
>
> For normal system, the dma_addr[1] in 'struct page' is not
> used, so we can reuse dma_addr[1] for storing frag count,
> which means how many frags this page might be splited to.
>
> In order to simplify the page frag support in the page pool,
> the PAGE_POOL_DMA_USE_PP_FRAG_COUNT macro is added to indicate
> the 32 bit systems with 64 bit dma, and the page frag support
> in page pool is disabled for such system.
>
> The newly added page_pool_set_frag_count() is called to reserve
> the maximum frag count before any page frag is passed to the
> user. The page_pool_atomic_sub_frag_count_return() is called
> when user is done with the page frag.
>
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
>  include/linux/mm_types.h | 18 +++++++++++++-----
>  include/net/page_pool.h  | 41 ++++++++++++++++++++++++++++++++++-------
>  net/core/page_pool.c     |  4 ++++
>  3 files changed, 51 insertions(+), 12 deletions(-)
>

<snip>

> +static inline long page_pool_atomic_sub_frag_count_return(struct page *page,
> +                                                         long nr)
> +{
> +       long frag_count = atomic_long_read(&page->pp_frag_count);
> +       long ret;
> +
> +       if (frag_count == nr)
> +               return 0;
> +
> +       ret = atomic_long_sub_return(nr, &page->pp_frag_count);
> +       WARN_ON(ret < 0);
> +       return ret;
>  }
>

So this should just be an atomic_long_sub_return call. You should get
rid of the atomic_long_read portion of this as it can cover up
reference count errors.

  reply	other threads:[~2021-07-20 15:54 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20  3:35 [PATCH rfc v6 0/4] add frag page support " Yunsheng Lin
2021-07-20  3:35 ` [PATCH rfc v6 1/4] page_pool: keep pp info as long as page pool owns the page Yunsheng Lin
2021-07-20  3:35 ` [PATCH rfc v6 2/4] page_pool: add interface to manipulate frag count in page pool Yunsheng Lin
2021-07-20 15:43   ` Alexander Duyck [this message]
2021-07-21  8:15     ` Yunsheng Lin
2021-07-21 14:06       ` Alexander Duyck
2021-07-22  8:07         ` Yunsheng Lin
2021-07-22 15:18           ` Alexander Duyck
2021-07-23 11:12             ` Yunsheng Lin
2021-07-23 16:08               ` Alexander Duyck
2021-07-24 13:07                 ` Yunsheng Lin
2021-07-25 16:49                   ` Alexander Duyck
2021-07-27  7:54                     ` Yunsheng Lin
2021-07-27 18:38                       ` Alexander Duyck
2021-08-02  9:17                         ` Yunsheng Lin
2021-07-20  3:35 ` [PATCH rfc v6 3/4] page_pool: add frag page recycling support " Yunsheng Lin
2021-07-20  3:35 ` [PATCH rfc v6 4/4] net: hns3: support skb's frag page recycling based on " Yunsheng Lin

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