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AJvYcCVMPl66TtX+V7y60xkJ/SzSO6bsdzvnjXlYcrnm9hN7CjIwMwDFuIMxtRwCiXAY4+asJo4ks2YifOkgLdvd76Z/wGM= X-Gm-Message-State: AOJu0YyQ6G4r+9c6oE18AwhjWBvKAGJfIlAL6ANowmX6dulrvLEOTT6y 6oIroev2AJ3vtzXhvI0PSMy7mpWAM9XmJn/jrtnPHSYK3N+Z9TDI2t51bLbpUGAnbkMy21NLS7d lSILabDS+J9+SIFon2J++VRx2oaNDPx2iukLVfA== X-Google-Smtp-Source: AGHT+IFhphzHdN0yMB659krxKIOe8jsISb3/tPe7DvSi5zNy0rhMzQJ/Jny1q2PhN4s5WLSuKKXCIpvd50AQNZZKwJ8= X-Received: by 2002:a9d:4d0d:0:b0:6e4:7ead:db99 with SMTP id n13-20020a9d4d0d000000b006e47eaddb99mr465307otf.33.1708642719625; Thu, 22 Feb 2024 14:58:39 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Pasha Tatashin Date: Thu, 22 Feb 2024 17:58:02 -0500 Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] Hugetlb Unifications To: Matthew Wilcox Cc: Peter Xu , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, James Houghton , Muchun Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8C6B114000F X-Stat-Signature: wzmyrh8ubybhwptczdrjax1b6ff6nrij X-HE-Tag: 1708642720-114785 X-HE-Meta: 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 bryg7Ooa Nr6k0Xl8rcchIzFS9ouU5vXCW8TiyjL1anCeTlOAsInI/7/k= 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 Thu, Feb 22, 2024 at 5:32=E2=80=AFPM Matthew Wilcox wrote: > > On Thu, Feb 22, 2024 at 05:16:44PM -0500, Pasha Tatashin wrote: > > However, we must also ensure compatibility with the interfaces and > > features unique to hugetlb, such as boot-time reservation and vmemap > > optimizations. Generalizing these features could potentially lead to > > memory savings in THP as well. > > In a memdesc world, how much value is there in vmemmap? At 8 bytes per > page, memmap occupies 4kB for 2MB and 2MB for 1GB. So there's no way > to save memory for a 2MB allocation, and saving 2MB per 1GB page is > ... not a huge win any more. Let's say you have a 64GB machine with > 50GB tied up in 1GB pages, we'll end up saving 100MB on a 64GB machine > which doesn't seem all that compelling? I agree that memdesc may eliminate the need for vmemmap optimizations. However, do we want to introduce regressions before transitioning to a memdesc world? Companies are currently saving petabytes of memory with vmemmap optimizations. > I do have a proposal for further compressing memmap, but it requires > doing memdesc first, so I'm reluctant to discuss it before we've done > memdescs. I have to have something to talk about at LSFMM'26 after all.