linux-kernel - Re: [PATCH v2 0/6] rds: rdma: Add ability to force GFP

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Date: Tue, 21 May 2024 07:24:03 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Håkon Bugge <haakon.bugge@...cle.com>
Cc: linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, rds-devel@....oracle.com,
	Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
	Saeed Mahameed <saeedm@...dia.com>,
	Tariq Toukan <tariqt@...dia.com>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
	Allison Henderson <allison.henderson@...cle.com>,
	Manjunath Patil <manjunath.b.patil@...cle.com>,
	Mark Zhang <markzhang@...dia.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Shiraz Saleem <shiraz.saleem@...el.com>,
	Yang Li <yang.lee@...ux.alibaba.com>
Subject: Re: [PATCH v2 0/6] rds: rdma: Add ability to force GFP_NOIO

On Wed, May 15, 2024 at 02:53:36PM +0200, Håkon Bugge wrote:
> This series enables RDS and the RDMA stack to be used as a block I/O
> device. This to support a filesystem on top of a raw block device
> which uses RDS and the RDMA stack as the network transport layer.
> 
> Under intense memory pressure, we get memory reclaims. Assume the
> filesystem reclaims memory, goes to the raw block device, which calls
> into RDS, which calls the RDMA stack. Now, if regular GFP_KERNEL
> allocations in RDS or the RDMA stack require reclaims to be fulfilled,
> we end up in a circular dependency.

Use of network block devices or file systems from the local system
simply isn't supported in the Linux reclaim hierchary.  Trying to
hack in through module options for code you haven't even submitted
is a complete nogo.

NAK.