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b=X7+8ljZag9MrMdygB/e5mTshdnVjmpMziL5L0xJEcDaZY8DYtpt7fNbFPgA/SVWxt 2Yh0hgP7jPhR4y4DTAfUd7sG7e6+xC2ORhALpoGls/i+F1610naxJf2JBqPnsH0vRo 3TI5FZu+7LSxVki7fAOtVyXq5W/yD/oiOLIoDrLDpIHtlv2u2BWt0N6DCLcXSWqZLf HFdXaNg1GpqjOxf3kjwOKadK3E2omKDA/UhFkZQPHIyvJUbuUdf1ddUoYVIB6g2X3x KtPOM60g96iMDCSmVxW/UHsImBJvRfb6qGIuTwccVssytmjoNmwxqxyfnb2ncw3Q+5 pZXUfVZwnSGlA== Date: Tue, 22 Apr 2025 11:35:17 +0300 From: Mike Rapoport To: Qu Wenruo Cc: Ingo Molnar , Borislav Petkov , Linux Memory Management List , LKML , Dave Hansen , x86-ml Subject: Re: Kernel 6.15-rc2 unable to boot on 32bit x86 with PAE Message-ID: References: <4599013d-bc74-4f81-9db7-070806ea9162@gmx.com> <20250418160515.GAaAJ4O2HnktVgmZ1v@fat_crate.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 0744D40003 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: epjy35xy4soidb4aq5bmcyj6rm13kkm4 X-HE-Tag: 1745310924-143877 X-HE-Meta: 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 W9gTgrxx hlYsxM2S/AfnDUyyLV23a9kzkCVrbOlj1wYgw8xTDdYOdLBfUuKZKSNtVcxFwwypAGUwf1BbSWoYdYK0MnSLaRFZ/b0WM+qnu4OKdIEqhBFf1liL9SomTnGhmKlPf+Fodiz3yTBl8lM+m7VKOOtj0vPYuHbMvKiRU34Xtsw9v6DltfoD0pU/XWMvBMjs7vv2ruxjrm6RGEGxwETqCrPjqZ3170Z5mPAKnJxmadn0plU47ihwGROexq9zeTWXnGY3QtIpFJrxsxCPJ1k7bNJ47/9PnJf8uiFlSZSxGw7rYL/IGNrU= 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 Tue, Apr 22, 2025 at 05:02:55PM +0930, Qu Wenruo wrote: > > > 在 2025/4/22 16:30, Ingo Molnar 写道: > > > > * Borislav Petkov wrote: > > > > > On Fri, Apr 18, 2025 at 08:31:23PM +0930, Qu Wenruo wrote: > > > > Hi, > > > > > > > > Recently I'm testing a situation where highmem is involved, thus I'm > > > > building the latest 32bit x86 with HIGHMEM and PAE, and run it inside a qemu > > > > VM. > > > > > > Does that fix it: > > > > > > https://git.kernel.org/tip/1e07b9fad022e0e02215150ca1e20912e78e8ec1 > > > > > > ? > > > > That commit caused other problems - the best fix we have right now is: > > > > https://git.kernel.org/tip/83b2d345e1786fdab96fc2b52942eebde125e7cd > > Thanks, I'll take a try again. > > But considering how rare 32bit + highmem systems are nowadays, I still have > one questions/concern: > > - How to make sure we really got highmems? > The kernel docs only mention that highmems need temporary mapping, > and proper kmap/kunmap() handling. > > But I still didn't have a straightforward idea of how to verify, > without adding manual ftrace events when a highmem page is hit. > > E.g. free only shows 3GB memory even if I enabled highmem + PAE. Without HIGHMEM it would be less than 900M. You can look for "HIGHMEM available" and "Memory: n/m available" in the kernel log to see how much highmem is there. > Since HIGHMEM64G is removed, I'd expect to get some values more like > 4G instead? There are some gaps under 4G, so it's surely less that 4G of usable memory there. > Thanks, > Qu -- Sincerely yours, Mike.