From: Andrew Morton <akpm@linux-foundation.org>
To: Arjun Roy <arjunroy.kdev@gmail.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, arjunroy@google.com, shakeelb@google.com,
edumazet@google.com, soheil@google.com, kuba@kernel.org,
mhocko@kernel.org, hannes@cmpxchg.org, shy828301@gmail.com,
guro@fb.com
Subject: Re: [mm, net-next v2] mm: net: memcg accounting for TCP rx zerocopy
Date: Wed, 17 Mar 2021 20:21:23 -0700 [thread overview]
Message-ID: <20210317202123.7d2eaa0e54c36c20571a335c@linux-foundation.org> (raw)
In-Reply-To: <20210316013003.25271-1-arjunroy.kdev@gmail.com>
On Mon, 15 Mar 2021 18:30:03 -0700 Arjun Roy <arjunroy.kdev@gmail.com> wrote:
> From: Arjun Roy <arjunroy@google.com>
>
> TCP zerocopy receive is used by high performance network applications
> to further scale. For RX zerocopy, the memory containing the network
> data filled by the network driver is directly mapped into the address
> space of high performance applications. To keep the TLB cost low,
> these applications unmap the network memory in big batches. So, this
> memory can remain mapped for long time. This can cause a memory
> isolation issue as this memory becomes unaccounted after getting
> mapped into the application address space. This patch adds the memcg
> accounting for such memory.
>
> Accounting the network memory comes with its own unique challenges.
> The high performance NIC drivers use page pooling to reuse the pages
> to eliminate/reduce expensive setup steps like IOMMU. These drivers
> keep an extra reference on the pages and thus we can not depend on the
> page reference for the uncharging. The page in the pool may keep a
> memcg pinned for arbitrary long time or may get used by other memcg.
>
> This patch decouples the uncharging of the page from the refcnt and
> associates it with the map count i.e. the page gets uncharged when the
> last address space unmaps it. Now the question is, what if the driver
> drops its reference while the page is still mapped? That is fine as
> the address space also holds a reference to the page i.e. the
> reference count can not drop to zero before the map count.
What tree were you hoping to get this merged through? I'd suggest net
- it's more likely to get tested over there.
>
> ...
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
These changes could be inside #ifdef CONFIG_NET. Although I expect
MEMCG=y&&NET=n is pretty damn rare.
next prev parent reply other threads:[~2021-03-18 3:21 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 1:30 [mm, net-next v2] mm: net: memcg accounting for TCP rx zerocopy Arjun Roy
2021-03-18 3:21 ` Andrew Morton [this message]
2021-03-22 21:19 ` Arjun Roy
2021-03-16 4:16 Arjun Roy
2021-03-16 4:20 ` Arjun Roy
2021-03-16 4:29 ` Shakeel Butt
2021-03-16 6:22 ` Arjun Roy
2021-03-16 6:28 ` Arjun Roy
2021-03-16 21:02 ` Jakub Kicinski
2021-03-16 10:26 ` Johannes Weiner
2021-03-17 6:05 ` Arjun Roy
2021-03-17 22:12 ` Johannes Weiner
2021-03-22 21:35 ` Arjun Roy
2021-03-23 17:01 ` Johannes Weiner
2021-03-23 18:42 ` Arjun Roy
2021-03-24 18:25 ` Shakeel Butt
2021-03-24 22:21 ` Arjun Roy
2021-03-23 14:34 ` Michal Hocko
2021-03-23 18:47 ` Arjun Roy
2021-03-24 9:12 ` Michal Hocko
2021-03-24 20:39 ` Arjun Roy
2021-03-24 20:53 ` Shakeel Butt
2021-03-24 21:56 ` Michal Hocko
2021-03-24 21:24 ` Johannes Weiner
2021-03-24 22:49 ` Arjun Roy
2021-03-25 9:02 ` Michal Hocko
2021-03-25 16:47 ` Johannes Weiner
2021-03-25 17:50 ` Michal Hocko
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