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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767797397; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=3JMmNWmMHBBTwh/RdlLu4xg38+1vNB2/LngywvTsD10=; b=TETO+lVpsN28EkzgRFG+IBMcjluh/LC66qZn2u/JzcXRCJ5CmAmOoQxUuDiDw+48ov5bvy J2yEHwKjMA1k1u2YTPxtsVa9vT/Tu5K7fPek6p04edGFnKQIkrXxoCYA+0AuBHQkZyq3A0 f33X5x1N7dt6z41pXKE4NeEYvziA/kA= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 100F56000A; Wed, 7 Jan 2026 14:49:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 46865C4CEF1; Wed, 7 Jan 2026 14:49:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767797396; bh=j66lzEexSpPcC3oYyLMGHNA0REWDjVJjs19BKH4bbz0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QisCsLODlmD8mwR9w0lTKYfsJJEsJtkfdC8i0SRZi8A4FyOzSL1LJaOfX164++05k eKxgdgbdRCvJYZu+jVHkK1beRfYXDyKmoRRCmYduZAl/SEUltttxQreUT7kXZPRUtQ Hmh4bnwFxOAVp1fie2HBHnhtF2rEBb5ol40wlSQDNt4I1uI9/ZUTsDrrpk37QZOXaJ zPl1B8lXa/X63dUXfxICcCkGwvR+AExXfQw1RHxHPmq7/QbfwOon7i2q8ZNAJAG7Sx EMrSTTOs7nTbbMrrG3iQWoHDvmEV/IvVklV2PMEu/5vcnaN2M15RviZLWIjb2GqJj1 30lvLfERPC0HQ== Message-ID: <02acb8f9-e60b-413c-a0d3-f1f8dda00ca3@kernel.org> Date: Wed, 7 Jan 2026 09:49:55 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/2] NFSD: Add aggressive write throttling control To: Christoph Hellwig Cc: Mike Snitzer , linux-nfs@vger.kernel.org, Chuck Lever , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20251219141105.1247093-1-cel@kernel.org> <20251219141105.1247093-2-cel@kernel.org> <20260107075501.GA19005@lst.de> <20260107144243.GA15228@lst.de> Content-Language: en-US From: Chuck Lever Organization: kernel.org In-Reply-To: <20260107144243.GA15228@lst.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A916C140010 X-Rspamd-Server: rspam10 X-Stat-Signature: cmgu98xtphp8i8y36odz84zty61kdktt X-HE-Tag: 1767797397-857016 X-HE-Meta: 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 DoKrbm4Z A9hf4N9Yun6XH7szI8a+uLrYe+yQ/8L+egB5l6EZSrvBYEToKqDGO+Ls6MZYdbkY+lQglFg5nwlO+79i3V0G5tzmYrF6tklGO+KQbu1nXjE31/zwISSdYpo8NqqIl5KhAfpwTPCCetBR3m2Go4/g553h1DsliXaDEvR3/Z52dKh1v+RYcZ3vZTKzQeQ6BeEzHOSRnu+jVduMEgNkNakAdbdVkPcxOSjGwGT8+pfgEdybMcscPUSYLwiEK6N7+8xYpjKFXOIugTBmHnaShVOM1PyS+l1PiwComcbLC X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/7/26 9:42 AM, Christoph Hellwig wrote: > 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? Well it might not be different. But at this point I don't think we know enough about the problem to say one way or another. I'm just trying to gather more experimental evidence about what is happening. -- Chuck Lever