From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0857344C51B; Fri, 25 Sep 2026 10:03:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790330593; cv=none; b=Je/VMl7AAiqUbG1dXb3ZW1xp0md1ScDXYjrRw0Or5iTLJ9meVOXzic7PtuJqhDDpjosujZ5vzWdCQ0fTY1okFxCbw4yz7soLRRcldDJFYFlesbKd/vHaTJXnPRgR7yCkWGgMqTuWL08QnldJWsUzVgn0yqirntquEfD/j+FqQ+g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790330593; c=relaxed/simple; bh=ufSOht/EsVEwLyh1sGJfcm8oa8yUigqSlnx3xRbFZu4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cWRxuqdCXv1JAdTgkFyjnjwmr64mLecBrYOJY70g0BQkRk/FgTcH3KGT3eRkqTpl1R9NY0izDJ5wOKiYrCAXf1lpT2VFFKTUbUeuohsYRt9uZRBOxbHH2uSk3KH0SnmRQ5+ItKPq8SbvPTe9CIfTd6tt/Y5YrW9NrsKrlVmzNzk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZQlSLR9x; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZQlSLR9x" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63CFB1F000FF; Fri, 25 Sep 2026 10:03:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790330591; bh=t36CornOt9N5L78VQ17XppVwwpYO+WRPIyNlZItd53Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZQlSLR9xHXZe3ovZL+O5SGKyjwqcEF8nNNxUh9+RbSALwRy1mRLu+0iaqVxvv7UG4 N/+won6apca3urjKK4I4XdG06ZAghJ7L+zqCotK8m4XqWrxJm8KvOjlbjSOoRKKyaX Ptpcjp5BHXjx2ms/e+tGKMvGhuA5K2W6jvJNUw2FEXMw7zc+uGxkpXMnjQaJ89GUxR ki3FLSpW9m9gUf3bEYg5P1gSA6Q1o7wdaulQwKazp5orcmaWrCljp9Wy4yo4ZdOqL6 mo6nouhIG3E9BCEYv+mMLrVQkcpPZ+uLequRrGGdIsJR/HYkhfbJQHpI0vNCvNUiJK gU35NHdAbIvAg== Message-ID: <59c4417d-b62b-4b40-9efb-e704b4162573@kernel.org> Date: Fri, 25 Sep 2026 12:03:04 +0200 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [FYI] DAMON and virtio-balloon in DeepSeek's DSec paper To: Lance Yang , muchun.song@linux.dev, research@deepseek.com Cc: sj@kernel.org, mst@redhat.com, damon@lists.linux.dev, linux-mm@kvack.org, virtualization@lists.linux.dev, ryncsn@gmail.com, kunwu.chan@gmail.com, lianux.mm@gmail.com, baohua@kernel.org, xueyuan.chen21@gmail.com References: <9f63d60c-913e-4e79-9d28-890dd48ef713@kernel.org> <20260925081504.23569-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/25/26 10:15, Lance Yang wrote: > +Cc DeepSeek and Muchun > > On Fri, Sep 25, 2026 at 09:04:41AM +0200, David Hildenbrand (Arm) wrote: >> On 9/25/26 07:44, Lance Yang wrote: >>> Hi all, >>> >>> I was reading DeepSeek's new DSec paper[1] and found a nice use of DAMON >>> and virtio-balloon: >>> >>> With this kind of workload, an agent may read a file once and never touch >>> it again, while those pages remain in the guest page cache. Without memory >>> pressure in the guest, they can stay cached even though the host would >>> like that memory back ... >>> >>> The trick is DAMON + virtio-balloon free-page reporting :) DAMON reclaims >> >> Heh, I read "virtio-balloon" and thought "balloon inflation/deflation, what year >> is it?!". Free-page reporting makes much more sense. >> >>> cold file pages from the guest page cache; buddy gets a chance to coalesce >>> them into reportable blocks, and virtio-balloon passes those blocks to >>> Firecracker. Firecracker can then drop the host backing with MADV_DONTNEED. >> >> When I was at RH we were looking at this issue as well. virtio-pmem was one way >> of avoiding the page cache in VM entirely. But it has its own limitations. > > YES, they enable virtio-pmem with DAX for the read-only EROFS base-image > and toolkit layers, while using DAMON with balloon free-page reporting to > reclaim cold file pages from the guest page cache on larger writable disks. > > They also point out that the guest must allocate struct page metadata for > the entire pmem-backed address range. So virtio-pmem is not free either :) > > BTW, Muchun recently posted a pretty cool series for exactly that: > > https://lore.kernel.org/linux-mm/20260903122128.12264-1-songmuchun@bytedance.com/ Yes, that will be helpful in that regard. > > (It shares vmemmap backing until a DAX fault needs private metadata, > avoiding the full per-PFN cost up front.) > > I have a feeling the DeepSeek team will be watching this one closely :P ;) -- Cheers, David