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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rdHbh-00000004tlg-49Vt; Thu, 22 Feb 2024 22:31:58 +0000 Date: Thu, 22 Feb 2024 22:31:57 +0000 From: Matthew Wilcox To: Pasha Tatashin Cc: Peter Xu , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, James Houghton , Muchun Song Subject: Re: [LSF/MM/BPF TOPIC] Hugetlb Unifications Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 2E03140015 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 8ah56crtu15p6kntnak6czu6a67tishm X-HE-Tag: 1708641125-949961 X-HE-Meta: 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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 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 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.