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Date:   Tue, 18 Aug 2020 09:00:10 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Cong Wang <xiyou.wangcong@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>, Coly Li <colyli@suse.de>,
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Subject: Re: [PATCH v5 1/3] net: introduce helper sendpage_ok() in
 include/linux/net.h
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On Mon, Aug 17, 2020 at 12:12:12PM -0700, Cong Wang wrote:
> 
> So netdev people will have to understand and support PageSlab() or
> page_count()?

Yes.  As they came up with that contrived rule what is acceptable
for sendpage.  No one else really knows and other subsystems like the
block layer are perfectly fine with it.

> 
> If it is unusual even for mm people, how could netdev people suppose
> to understand this unusual mm bug? At least not any better.

It is not a mm bug, it is a networking quirk.