From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 30A1E38BDDB; Mon, 19 Jan 2026 15:50:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768837812; cv=none; b=o9HFVJ4qhxP+R3DHBZliPaDgU7lNeHVJdCqbGbBGeGFvuNjsJRqMaJABR/4fEteHhp/XB7Dqu5c7NnKVPl6z55pEo9eDk7pofQ3sLMBlrS3q/QBsXW6BR6bi72W0ILmT9qW0N7HLPWoN15rwEEn1oPaV3Tqo28BJzwi0URaNMBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768837812; c=relaxed/simple; bh=Ge9a4W+ScNHnrmyDYC412nampeZPIhF0MI75Naq8xpA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JCxTljdh46YtrLs0je6tCnIJXKOElTFmNrEMha+ZalJ55k0A9hh/uTRPHcLMkjspZ0XCtUcfQt4ba69kgXk6jcZm3l3n+OwPbrL+xT50yRkc+cCl9uRHC7meHPhR5I1CwO/y/82de6YWnJA0E748Av/B06DG6bypVKh1XrDykrQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dZ/SV3dl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dZ/SV3dl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 936F6C116C6; Mon, 19 Jan 2026 15:50:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768837811; bh=Ge9a4W+ScNHnrmyDYC412nampeZPIhF0MI75Naq8xpA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dZ/SV3dlZW495MXI0aLbck5VMqdHMguCknlACk68Up73QNrFUPkpdQGBmflfG5/su zP6y2wW61oNvnOOxYqAQLYsv764wrQHmFOr3aeVppps6TjdlV6sZtrMzjAbF5BIlxm W7Rf0jVDs6dFbl+awCQofsyR5vtwyUfNjpUVPfDM/GsOTGgW5/HXuaMdfoqL6f8XME /l4rjY7Tz76OtC8NUOYwxogDSm8cGu85syhWJfYw5CdXIAz03D39n6y/5OIVu51IzZ yBmr0ZJswUsan6j6SF7J1EnfZZADmnytyZccmiiCjs4qLMGwjw1CfO68p4fmNRZRYz CGxfvycWg1+9A== Message-ID: <6c3f8061-302e-40c1-829b-2f8555bee70c@kernel.org> Date: Mon, 19 Jan 2026 16:50:06 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] virtio_balloon: Support wait on ACK for hinting To: Jack Thomson , mst@redhat.com, jasowang@redhat.com Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, kalyazin@amazon.co.uk, xmarcalx@amazon.co.uk, jackabt@amazon.com References: <20260119154236.39412-1-jackabt.amazon@gmail.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/19/26 16:42, Jack Thomson wrote: > From: Jack Thomson > > This RFC patch adds a new virtio feature for the virtio-balloon driver > during free page hinting, which will wait on device ack before > committing the range to the free_page_list. The reason for the change is > it allows the device to modify this range without it being reclaimed > from the free_page_list before the ack is sent. As expected, testing > shows this adds overhead to the hinting run duration, increasing it by > ~30% with our Firecracker setup. Currently free page hinting is used > mainly for live migration, but this would open it up for a new use-case. > > We would like to leverage this with MADV_DONTNEED to reduce RSS of a > guest. We'd like to use hinting because of the flexibility of control it > brings compared to reporting, allowing memory to be reclaimed in > deterministic periods. Can you elaborate in more detail why you don't simply use reporting, like QEMU? Could you instead see optimizations being done to reporting that could make it fly for your use case? Hinting is a rather special case thing only used for reducing VM migration time in QEMU AFAIR. -- Cheers David