linux-kernel - RE: [PATCH v5] net/mlx5: Reclaim max 50K pages at once

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Message-ID: <666c79de2adf4959bd167f3f1c45e1fc@AcuMS.aculab.com>
Date: Fri, 28 Jun 2024 15:44:15 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Anand Khoje' <anand.a.khoje@...cle.com>, Jesse Brandeburg
	<jesse.brandeburg@...el.com>, "linux-rdma@...r.kernel.org"
	<linux-rdma@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: "saeedm@...lanox.com" <saeedm@...lanox.com>, "leon@...nel.org"
	<leon@...nel.org>, "tariqt@...dia.com" <tariqt@...dia.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [PATCH v5] net/mlx5: Reclaim max 50K pages at once

...
> The way Mellanox ConnectX5 driver handles 'release of allocated pages
> from HCA' or 'allocation of pages to HCA', is by sending an event to the
> host. This event will have number of pages in it. If the number is
> positive, that indicates HCA is requesting that number of pages to be
> allocated. And if that number is negative, it is the HCA indicating that
> that number of pages can be reclaimed by the host.

A one line comment would do.
Possibly even negating the be32toh() result?

> In this patch we are restricting the maximum number of pages that can be
> reclaimed to be 50000 (effectively this would be -50000 as it is
> reclaim). This limit is based on the capability of the firmware as it
> cannot release more than 50000 back to the host in one go.

Hang on, why are you soft limiting it to the hard limit?
I thought the problem was that releasing a lot of pages took a long
time and 'stuffed' other time-critical tasks.

The only way to resolve that would seem to be to defer the actual freeing
to a low (or at least normal user) priority thread.
You would definitely want to get out of 'softint' context.
(Which is out of napi unless forced to be threaded - and that only really
works if you force the threads under the RT scheduler.)

	David

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