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Sun, 7 May 2023 19:43:33 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id 56ADB10D349; Mon, 8 May 2023 02:43:30 +0300 (+03) Date: Mon, 8 May 2023 02:43:30 +0300 From: "Kirill A. Shutemov" To: Matthew Wilcox Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [LSF/MM/BPF] Whither Highmem? Message-ID: <20230507234330.cnzbumof2hdl4ci6@box.shutemov.name> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 59imatwbord1trtgsepzryntyqe3nfyg X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: EBEBA100004 X-HE-Tag: 1683503014-179705 X-HE-Meta: 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 DQbFAVvw nlz/Z9qwVRfZgN++xuCK4xdNLpMJzbMroY8VOVqEXjaR6StqT5qbi7hwawx7LZ7VHs8lHuXva7SkUgJ4C3Cf3tZN5XdgSILe45LqYm4lVyYlFjk7UyDmlT5SNobfxB6vmZ4cTZysQ0wrljG8FJpB606UzLpISdHSDxL5mYKDGXPOqe/rIZObAfN+lFJGfoyFaI1mfzlr2uKo+jYToB1Zq5a7ZbRmb3lcI93CmLelQMg5s8AVH6t2WFdARCTKKMkolYI5HGj3pF5dvU5lVb1KBag6ZXiJY2LXkNzjhmcTmDqP0NLaOLhQLF0eRjt8D0zu5UGUN3Aph2+brxtqGjHA6EXvglQ== 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: On Mon, May 08, 2023 at 12:20:42AM +0100, Matthew Wilcox wrote: > > I see there's a couple of spots on the schedule open, so here's something > fun we could talk about. > > Highmem was originally introduced to support PAE36 (up to 64GB) on x86 > in the late 90s. It's since been used to support a similar extension > on ARM (maybe other 32-bit architectures?) > > Things have changed a bit since then. There aren't a lot of systems > left which have more than 4GB of memory _and_ are incapable of running a > 64-bit kernel. Actual limit is lower. With 3G/1G userspace/kernel split you will have somewhere about 700Mb of virtual address space for direct mapping. But, I would like to get rid of highmem too. Not sure how realistic it is. -- Kiryl Shutsemau / Kirill A. Shutemov