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Date: Wed, 7 Jan 2026 15:42:43 +0100
From: Christoph Hellwig <hch@lst.de>
To: Chuck Lever <cel@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Mike Snitzer <snitzer@kernel.org>,
	linux-nfs@vger.kernel.org, Chuck Lever <chuck.lever@oracle.com>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH 1/2] NFSD: Add aggressive write throttling control
Message-ID: <20260107144243.GA15228@lst.de>
References: <20251219141105.1247093-1-cel@kernel.org> <20251219141105.1247093-2-cel@kernel.org> <20260107075501.GA19005@lst.de> <cb269767-688d-46f1-8d82-1fd6dc32e94d@kernel.org>
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On Wed, Jan 07, 2026 at 09:36:39AM -0500, Chuck Lever wrote:
> > What makes NFSD so special here vs say a userspace process with a bunch
> > of threads?  Also what is the actual problem we're trying to solve?
> 
> The problem, as I see it, is that the system is not providing enough
> backpressure to slow down noisy clients, allowing them to overwhelm
> the server's memory with UNSTABLE WRITE traffic.
> 
> This is the same issue, IMO, that Mike's direct I/O is attempting to
> address. Our implementation of UNSTABLE WRITE is a denial-of-service
> vector.

But how is this different from Samba or a userspace NFS server?