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by SJ0PR17MB4728.namprd17.prod.outlook.com (2603:10b6:a03:379::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6254.35; Tue, 4 Apr 2023 18:43:08 +0000 Received: from SJ0PR17MB5512.namprd17.prod.outlook.com ([fe80::7b97:62c3:4602:b47a]) by SJ0PR17MB5512.namprd17.prod.outlook.com ([fe80::7b97:62c3:4602:b47a%5]) with mapi id 15.20.6254.035; Tue, 4 Apr 2023 18:43:08 +0000 Date: Sat, 1 Apr 2023 06:51:01 -0400 From: Gregory Price To: Adam Manzanares Cc: Mike Rapoport , Kyungsan Kim , "lsf-pc@lists.linux-foundation.org" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-cxl@vger.kernel.org" , "viacheslav.dubeyko@bytedance.com" , "dan.j.williams@intel.com" , "seungjun.ha@samsung.com" , "wj28.lee@samsung.com" Subject: Re: RE: RE(2): FW: [LSF/MM/BPF TOPIC] SMDK inspired MM changes for CXL Message-ID: References: <20230331114525.400375-1-ks0204.kim@samsung.com> <20230404175754.GA633356@bgt-140510-bm01> Content-Type: text/plain; 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memory should be used for swap. I see a > swap device as storing pages in a manner that is no longer directly addressable > by the cpu. > > Migrating pages to a CXL device is a reasonable approach and I believe we > have the ability to do this in the page reclaim code. > The argument is "why do you need swap if memory itself is elastic", and I think there are open questions about how performant using large amounts of high-latency memory is. Think 1us-1.5us+ cross-rack attached memory. Does it make sense to use that as CPU-addressible and migrate it on first use? Isn't that just swap with more steps? What happens if we just use it as swap, is the performance all that different? I think there's a reasonable argument for exploring the idea at the higher ends of the latency spectrum. And the simplicity of using an existing system (swap) to implement a form of proto-tiering is rather attractive in my opinion. ~Gregory