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 1mH4ypWK X3YwwGwCKfKsUHl8A35x0N368PQ0KOGgIOoYrf2JqlxSOHvn7faQXPPHimzse5aCeHDaLShDDlZFfcJsBNZe4JYiosm9wLV/eQxi6Ibz1WLKdazuFf4bXBAbZQxxeAGOx5AOgbi+ZXDt3sE68HbxxatfGNmAjl5+pq1DpISxleAKPzmF0KJzfCi5E6kZ4YtBjIA65HQLHjaonK2fL2pPEZkMCpVEtFH8yyCqubWr4K2SFu8mZpZfUfZRNYDMgpc+C1ZY6 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 4/6/23 13:07, Andrew Morton wrote: > On Wed, 5 Apr 2023 21:05:15 -0700 John Hubbard wrote: > >> Although CONFIG_DEVICE_PRIVATE and hmm_range_fault() and related >> functionality was first developed on x86, it also works on arm64. >> However, when trying this out on an arm64 system, it turns out that >> there is a massive slowdown during the setup and teardown phases. >> >> This slowdown is due to lots of calls to WARN_ON()'s that are checking >> for pages that are out of the physical range for the CPU. However, >> that's a design feature of device private pages: they are specfically >> chosen in order to be outside of the range of the CPU's true physical >> pages. >> >> ... >> >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -1157,8 +1157,10 @@ int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node, >> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, >> struct vmem_altmap *altmap) >> { >> +/* Device private pages are outside of the CPU's physical page range. */ >> +#ifndef CONFIG_DEVICE_PRIVATE >> WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END)); > > For a simple expression like this to cause a "massive slowdown", I > assume the WARN is triggering. But changelog doesn't mention massive > dmesg spewage? Well, it should. Whoever wrote that needs to improve the changelog. :) > > Given Ard's comments, perhaps a switch to WARN_ON_ONCE() would suit? That would fix up the user-visible problems, which would be very nice. Meanwhile, I'm trying to sort out whether this really is a false positive for arm64. thanks, -- John Hubbard NVIDIA