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AJvYcCV/HTXHmW7YJGK25rYdZp26uQmWKFugGYa6a7vVsDBWpes6hWZVdCpmphyYhRoXX7ChvehNRFZLi+L0axKWRMm8F9I= X-Gm-Message-State: AOJu0YxK45rkZtIwXZ+bw5ajqauimWrX8Al3/eluDl1KTt5E0hU0vk64 qT43iTk6Prcj9KOoAWet+MzpF/YpexLGZ14FP7lCd6dticoR0FnSb9iNoFk0yAw= X-Google-Smtp-Source: AGHT+IGD3wO0ydBAxxlvkA4miE1+LF/l7SGE6Vt5MCRiu9Xb9EU7ECTxmWTT1y93q+YRYuMk77eE+Q== X-Received: by 2002:a2e:8045:0:b0:2df:7824:7d32 with SMTP id 38308e7fff4ca-2e5204b1e12mr168929241fa.50.1716115029910; Sun, 19 May 2024 03:37:09 -0700 (PDT) Received: from smtpclient.apple ([2a00:1370:81a4:8e0a:ddf8:74b1:36e3:738e]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-2e4d1515664sm30931751fa.93.2024.05.19.03.37.08 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 19 May 2024 03:37:09 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.8\)) Subject: Re: [Resend LSF/MM/BPF TOPIC] A case of a CXL compressed memory tier From: Viacheslav Dubeyko In-Reply-To: <29803911-8566-4fa5-b1d1-7e3def541d7c@nmtadam.samsung> Date: Sun, 19 May 2024 13:37:07 +0300 Cc: Yiannis Nikolakopoulos , "mhocko@suse.com" , Dan J Williams , "lsf-pc@lists.linux-foundation.org" , "linux-mm@kvack.org" , "linux-cxl@vger.kernel.org" , Angelos Arelakis , "Weiny, Ira" , "yiannis@zptcorp.com" Content-Transfer-Encoding: quoted-printable Message-Id: References: <29803911-8566-4fa5-b1d1-7e3def541d7c@nmtadam.samsung> To: Adam Manzanares X-Mailer: Apple Mail (2.3696.120.41.1.8) X-Rspamd-Queue-Id: E16B8120007 X-Stat-Signature: 1qq97pgrp4uapfnodbs9g6irpmzrdoii X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1716115031-8088 X-HE-Meta: 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 fnN86AkH 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 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 May 14, 2024, at 3:30 PM, Adam Manzanares = wrote: >=20 > On Tue, May 14, 2024 at 01:43:29PM +0200, Yiannis Nikolakopoulos = wrote: >> Hello all, >>=20 >> This is almost literally last minute and the work itself is only >> getting started. But since I'm virtually attending, I thought to give >> it a shot in case it is of interest. >>=20 >> Background: at ZeroPoint Technologies we are developing inline memory >> compression IP. Currently we are focusing on CXL type 3 devices >> (memory expanders), effectively introducing a compressed memory tier >> (i.e. fulfilling the OCP specification "Hyperscale CXL Tiered = Memory >> Expander Specification=E2=80=9D). >>=20 >> To utilize the memory saved due to compression, we oversubscribe the >> Device Physical Address Space (DPA) in addition to some custom .io >> interfaces. If there is interest, I would be glad to present these >> APIs and how the host's point of view changes compared to a = "typical" >> memory tiering system. The goal would be to get some early feedback >> and direction for our upstream driver development, before we start >> pushing the first RFCs. >=20 > I am interested in understanding the interfaces and how the memory = will be > consumed and presented by the MM subsystem. It is my understanding = that > we have a 30 min slot for CXL related topics open this morning. I = think this=20 > would be a good fit. >=20 After attending the talk, I think it=E2=80=99s really need to = clarify/justify the use-cases that could benefit by employing this approach. Maybe, I am missing something here. But, I think that compaction scheme = could be a potential pain. I mean even one application allocates and = deallocates/frees memory very frequently. If we place several compressed data portions into some = physical granularity (for example, 4K or any other size), then freeing operation can = definitely creates holes or introduce fragmentation. Memory operations are really fast and such = fragmentation could be really significant. And such fragmentation could be more critical for = the case of multiple applications and multiple hosts. It sounds for me that this approach = could really require a GC or a defragmentation subsystem. But such subsystem could introduce = additional latency or could affect applications=E2=80=99 performance. So, maybe, smart = allocation policy can help here, otherwise, it needs to introduce a really smart and efficient = defragmentation or GC policy. Definitely, it=E2=80=99s interesting problem to think about. :) Thanks, Slava.