Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
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>,
	Netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH rfc v2 2/5] page_pool: add interface for getting and setting pagecnt_bias
Date: Sat, 10 Jul 2021 09:55:10 -0700	[thread overview]
Message-ID: <CAKgT0UcRqRcj_zewRUH4Qe-AP_ykArK0hu76kcw2xjtvkTw07g@mail.gmail.com> (raw)
In-Reply-To: <1625903002-31619-3-git-send-email-linyunsheng@huawei.com>

On Sat, Jul 10, 2021 at 12:44 AM Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> As suggested by Alexander, "A DMA mapping should be page
> aligned anyway so the lower 12 bits would be reserved 0",
> so it might make more sense to repurpose the lower 12 bits
> of the dma address to store the pagecnt_bias for elevated
> refcnt case in page pool.
>
> As newly added page_pool_get_pagecnt_bias() may be called
> outside of the softirq context, so annotate the access to
> page->dma_addr[0] with READ_ONCE() and WRITE_ONCE().
>
> Other three interfaces using page->dma_addr[0] is only called
> in the softirq context during normal rx processing, hopefully
> the barrier in the rx processing will ensure the correct order
> between getting and setting pagecnt_bias.
>
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
>  include/net/page_pool.h | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 8d7744d..5746f17 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -200,7 +200,7 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
>
>  static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
>  {
> -       dma_addr_t ret = page->dma_addr[0];
> +       dma_addr_t ret = READ_ONCE(page->dma_addr[0]) & PAGE_MASK;
>         if (sizeof(dma_addr_t) > sizeof(unsigned long))
>                 ret |= (dma_addr_t)page->dma_addr[1] << 16 << 16;
>         return ret;
> @@ -208,11 +208,31 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
>
>  static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
>  {
> -       page->dma_addr[0] = addr;
> +       unsigned long dma_addr_0 = READ_ONCE(page->dma_addr[0]);
> +
> +       dma_addr_0 &= ~PAGE_MASK;
> +       dma_addr_0 |= (addr & PAGE_MASK);

So rather than doing all this testing and clearing it would probably
be better to add a return value to the function and do something like:

if (WARN_ON(dma_addr_0 & ~PAGE_MASK))
    return -1;

That way you could have page_pool_dma_map unmap, free the page, and
return false indicating that the DMA mapping failed with a visible
error in the event that our expectionat that the dma_addr is page
aligned is ever violated.

> +       WRITE_ONCE(page->dma_addr[0], dma_addr_0);
> +
>         if (sizeof(dma_addr_t) > sizeof(unsigned long))
>                 page->dma_addr[1] = upper_32_bits(addr);
>  }
>
> +static inline int page_pool_get_pagecnt_bias(struct page *page)
> +{
> +       return (READ_ONCE(page->dma_addr[0]) & ~PAGE_MASK);

You don't need the parenthesis around the READ_ONCE and PAGE_MASK.

> +}
> +
> +static inline void page_pool_set_pagecnt_bias(struct page *page, int bias)
> +{
> +       unsigned long dma_addr_0 = READ_ONCE(page->dma_addr[0]);
> +
> +       dma_addr_0 &= PAGE_MASK;
> +       dma_addr_0 |= (bias & ~PAGE_MASK);
> +
> +       WRITE_ONCE(page->dma_addr[0], dma_addr_0);
> +}
> +
>  static inline bool is_page_pool_compiled_in(void)
>  {
>  #ifdef CONFIG_PAGE_POOL
> --
> 2.7.4
>

  reply	other threads:[~2021-07-10 16:55 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-10  7:43 [PATCH rfc v2 0/5] add elevated refcnt support for page pool Yunsheng Lin
2021-07-10  7:43 ` [PATCH rfc v2 1/5] page_pool: keep pp info as long as page pool owns the page Yunsheng Lin
2021-07-10  7:43 ` [PATCH rfc v2 2/5] page_pool: add interface for getting and setting pagecnt_bias Yunsheng Lin
2021-07-10 16:55   ` Alexander Duyck [this message]
2021-07-12  7:44     ` Yunsheng Lin
2021-07-10  7:43 ` [PATCH rfc v2 3/5] page_pool: add page recycling support based on elevated refcnt Yunsheng Lin
2021-07-10 17:24   ` Alexander Duyck
2021-07-12  7:54     ` Yunsheng Lin
2021-07-10 17:31   ` Alexander Duyck
2021-07-12  2:06     ` Yunsheng Lin
2021-07-12  3:30       ` Alexander Duyck
2021-07-10  7:43 ` [PATCH rfc v2 4/5] page_pool: support page frag API for page pool Yunsheng Lin
2021-07-10 17:43   ` Alexander Duyck
2021-07-12  7:57     ` Yunsheng Lin
2021-07-10  7:43 ` [PATCH rfc v2 5/5] net: hns3: support skb's frag page recycling based on " Yunsheng Lin
2021-07-10 15:40 ` [PATCH rfc v2 0/5] add elevated refcnt support for " Matteo Croce

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAKgT0UcRqRcj_zewRUH4Qe-AP_ykArK0hu76kcw2xjtvkTw07g@mail.gmail.com \
    --to=alexander.duyck@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=alobakin@pm.me \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=cong.wang@bytedance.com \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=elver@google.com \
    --cc=feng.tang@intel.com \
    --cc=fenghua.yu@intel.com \
    --cc=guro@fb.com \
    --cc=haokexin@gmail.com \
    --cc=hawk@kernel.org \
    --cc=hughd@google.com \
    --cc=ilias.apalodimas@linaro.org \
    --cc=jgg@ziepe.ca \
    --cc=john.fastabend@gmail.com \
    --cc=jonathan.lemon@gmail.com \
    --cc=kuba@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=linuxarm@openeuler.org \
    --cc=linyunsheng@huawei.com \
    --cc=mcroce@microsoft.com \
    --cc=mw@semihalf.com \
    --cc=netdev@vger.kernel.org \
    --cc=nogikh@google.com \
    --cc=peterx@redhat.com \
    --cc=peterz@infradead.org \
    --cc=salil.mehta@huawei.com \
    --cc=thomas.petazzoni@bootlin.com \
    --cc=vbabka@suse.cz \
    --cc=wenxu@ucloud.cn \
    --cc=will@kernel.org \
    --cc=willemb@google.com \
    --cc=willy@infradead.org \
    --cc=yisen.zhuang@huawei.com \
    --subject='Re: [PATCH rfc v2 2/5] page_pool: add interface for getting and setting pagecnt_bias' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).