linux-kernel - Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY

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Message-ID: <8ce78bd6-8142-2937-11fd-2e4a2b22d90c@gmail.com>
Date:   Wed, 25 Apr 2018 09:20:55 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for
 zerocopy receive



On 04/25/2018 09:04 AM, Matthew Wilcox wrote:

> If you don't zap the page range, any of the CPUs in the system where
> any thread in this task have ever run may have a TLB entry pointing to
> this page ... if the page is being recycled into the page allocator,
> then that page might end up as a slab page or page table or page cache
> while the other CPU still have access to it.

Yes, this makes sense.

> 
> You could hang onto the page until you've built up a sufficiently large
> batch, then bulk-invalidate all of the TLB entries, but we start to get
> into weirdnesses on different CPU architectures.
> 

zap_page_range() is already doing a bulk-invalidate,
so maybe vm_replace_page() wont bring serious improvement if we end-up doing same dance.

Thanks.