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From: Brian Norris <briannorris@chromium.org>
To: Jian-Hong Pan <jian-hong@endlessm.com>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	"David S . Miller" <davem@davemloft.net>,
	Larry Finger <Larry.Finger@lwfinger.net>,
	David Laight <David.Laight@aculab.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	"<netdev@vger.kernel.org>" <netdev@vger.kernel.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	linux@endlessm.com, Daniel Drake <drake@endlessm.com>,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH v3 1/2] rtw88: pci: Rearrange the memory usage for skb in RX ISR
Date: Thu, 15 Aug 2019 13:25:46 -0700
Message-ID: <CA+ASDXOgCHzAfyQDAGhkFZMO4UaXfrnpkN9a95jzfQY_L+EbAg@mail.gmail.com> (raw)
In-Reply-To: <20190710083825.7115-1-jian-hong@endlessm.com>

Hi all,

I realize this already is merged, and it had some previous review
comments that led to the decisions in this patch, but I'd still like
to ask here, where I think I'm reaching the relevant parties:

On Wed, Jul 10, 2019 at 1:43 AM Jian-Hong Pan <jian-hong@endlessm.com> wrote:
...
> This patch allocates a new, data-sized skb first in RX ISR. After
> copying the data in, we pass it to the upper layers. However, if skb
> allocation fails, we effectively drop the frame. In both cases, the
> original, full size ring skb is reused.
>
> In addition, by fixing the kernel crash, the RX routine should now
> generally behave better under low memory conditions.
>
> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=204053
> Signed-off-by: Jian-Hong Pan <jian-hong@endlessm.com>
> Cc: <stable@vger.kernel.org>
> ---
> v2:
>  - Allocate new data-sized skb and put data into it, then pass it to
>    mac80211. Reuse the original skb in RX ring by DMA sync.

Is it really wise to force an extra memcpy() for *every* delivery?
Isn't there some other strategy that could be used to properly handle
low-memory scenarios while still passing the original buffer up to
higher layers most of the time? Or is it really so bad to keep
re-allocating RTK_PCI_RX_BUF_SIZE (>8KB) of contiguous memory, to
re-fill the RX ring? And if that is so bad, can we reduce the
requirement for contiguous memory instead? (e.g., keep with smaller
buffers, and perform aggregation / scatter-gather only for frames that
are really larger?)

Anyway, that's mostly a long-term thought, as this patch is good for
fixing the important memory errors, even if it's not necessarily the
ideal solution.

Regards,
Brian

  parent reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-08  6:32 [PATCH] rtw88/pci: " Jian-Hong Pan
2019-07-08  7:23 ` Tony Chuang
2019-07-08  8:07   ` Jian-Hong Pan
2019-07-08  9:00     ` Tony Chuang
2019-07-08  9:18       ` David Laight
2019-07-08  8:36 ` David Laight
2019-07-08 18:01 ` Larry Finger
2019-07-09 10:20 ` [PATCH v2 1/2] rtw88: pci: " Jian-Hong Pan
2019-07-10  8:36   ` Tony Chuang
2019-07-10  8:54     ` Jian-Hong Pan
2019-07-09 10:21 ` [PATCH v2 2/2] rtw88: pci: Use DMA sync instead of remapping " Jian-Hong Pan
2019-07-09 16:15   ` Christoph Hellwig
2019-07-10  8:38     ` [PATCH v3 1/2] rtw88: pci: Rearrange the memory usage for skb " Jian-Hong Pan
2019-07-10  8:57       ` David Laight
2019-07-11  3:50         ` Jian-Hong Pan
2019-07-11  5:24           ` [PATCH v4 " Jian-Hong Pan
2019-07-11  5:24             ` [PATCH v4 2/2] rtw88: pci: Use DMA sync instead of remapping " Jian-Hong Pan
2019-07-11  5:30               ` Jian-Hong Pan
2019-07-11  5:28             ` [PATCH v4 1/2] rtw88: pci: Rearrange the memory usage for skb " Jian-Hong Pan
2019-07-24  6:13               ` Jian-Hong Pan
2019-07-24 11:49             ` Kalle Valo
2019-08-15 20:25       ` Brian Norris [this message]
2019-07-10  8:38     ` [PATCH v3 2/2] rtw88: pci: Use DMA sync instead of remapping " Jian-Hong Pan

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