From: "Jonathan Lemon" <jonathan.lemon@gmail.com>
To: "Eric Dumazet" <eric.dumazet@gmail.com>
Cc: Netdev <netdev@vger.kernel.org>, "Saeed Mahameed" <saeedm@mellanox.com>
Subject: Re: rtnl_lock() question
Date: Wed, 04 Sep 2019 09:38:08 -0700 [thread overview]
Message-ID: <C46053D2-6BF5-4CFE-BF76-32DDCAD7BC10@gmail.com> (raw)
In-Reply-To: <3164f8de-de20-44f7-03fb-8bc39ca8449e@gmail.com>
On 4 Sep 2019, at 0:39, Eric Dumazet wrote:
> On 9/3/19 11:55 PM, Jonathan Lemon wrote:
>> How appropriate is it to hold the rtnl_lock() across a sleepable
>> memory allocation? On one hand it's just a mutex, but it would
>> seem like it could block quite a few things.
>>
>
> Sure, all GFP_KERNEL allocations can sleep for quite a while.
>
> On the other hand, we may want to delay stuff if memory is under
> pressure,
> or complex operations like NEWLINK would fail.
>
> RTNL is mostly taken for control path operations, we prefer them to be
> mostly reliable, otherwise admins job would be a nightmare.
>
> In some cases, it is relatively easy to pre-allocate memory before
> rtnl is taken,
> but that will only take care of some selected paths.
The particular code path that I'm looking at is mlx5e_tx_timeout_work().
This is called on TX timeout, and mlx5 wants to move an entire channel
and all the supporting structures elsewhere. Under the rtnl_lock(), it
calls kvzmalloc() in order to grab a large chunk of contig memory, which
ends up stalling the system.
I suspect these large allocation should really be done outside the lock.
--
Jonathan
next prev parent reply other threads:[~2019-09-04 16:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-03 21:55 rtnl_lock() question Jonathan Lemon
2019-09-04 7:39 ` Eric Dumazet
2019-09-04 16:38 ` Jonathan Lemon [this message]
2019-09-04 23:23 ` Saeed Mahameed
2019-09-05 18:07 ` Rustad, Mark D
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