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[217.62.96.139]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b07830464f9sm78316966b.9.2025.09.09.18.06.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 18:06:03 -0700 (PDT) Message-ID: Date: Wed, 10 Sep 2025 03:06:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: torvalds@linux-foundation.org Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, alexander.sverdlin@gmail.com, andreas@gaisler.com, ankur.a.arora@oracle.com, arnd@arndb.de, chester.a.unal@arinc9.com, christophe.leroy@csgroup.eu, david@redhat.com, geert+renesas@glider.be, heiko@sntech.de, hpa@zytor.com, imx@lists.linux.dev, ira.weiny@intel.com, ksummit@lists.linux.dev, l.stach@pengutronix.de, linus.walleij@linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, lorenzo.stoakes@oracle.com, nm@ti.com, richard@nod.at, rppt@kernel.org, sergio.paracuellos@gmail.com, surenb@google.com, vbabka@suse.cz, willy@infradead.org References: Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout Content-Language: en-US From: =?UTF-8?Q?Ren=C3=A9_Herman?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250909_180606_706218_6F26EF8E X-CRM114-Status: GOOD ( 12.84 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > Well, while on x86 1GB systems did use highmem, they'd typically not > use very much of it. > > IOW, they'd have about 900MB as lowmem (ok, I think it was 896MB to > be exact), with something like 120MB highmem. > > So they'd either lose a bit of memory, or they'd use the 2G:2G > split. Right, 1G-128M of VMALLOC_RESERVE, but they didn't generally use 2G/2G but ever since it was introduced late in the 32-bit era VMSPLIT_3G_OPT, i.e., PAGE_OFFSET = 0xb0000000, i.e., 3G-256M/1G+256M. Although at the time the patches died an unceremonious death, 4G/4G patches for x86 were also around; I used to be a (conceptual) fan of them: it takes quite a number of TLB-flushes to suck more than highmem. Not one hint of clue if spectre/meltdown is applicable to these systems and if so, if they in fact do or should already be suffering through those same flushes anyway but maybe it'd be an option to dig those patches out of some archive somewhere. I promise I'll test them on an AMD Duron with 768MB RAM :) Rene.