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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 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 X-Stat-Signature: ejdkuib7bx6u433zwpsgckym3t7eo9n7 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 65CB6A0008 X-HE-Tag: 1790330592-308672 X-HE-Meta: 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 xakJGObk xzT0rGV+E/vPJkXQAc8tVbWGJy1Ny+U8H8+K2Jwf7hHhufrk6pwljftFtrm2Bua38IrHaLaETAk1f+rcBafoRCrqSgjWya2VC8m8DXio3a/Kx58K9IrsyoN60hxlrgaW/8QdEOdxlC1/O++GvvRMJYo6yBXw13UKpdbAC/cahbwMUmM7OstaQkM1SPJRFGCXP+TOFpXufV0taZgrXr2Rw/WW8NNe4HYB1WYZCq3+HXz+L2lrnCmeP0hMI2o4JVWB669a4T9TaEe9W7J03G1w/KaA48kqhoixfRlqrgp4XWbqJYAEs7BUQYBI84Qb4JVgrrt8yhc8cM8OPvyLdDL9zE/hom6KhK4mHBYvA8Wa058NFNKcbiebjHKuHLfc83Ccc0SJr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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