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b=lp3q0TXLLJy3nqhzUHsU4dOWZjR3u2CraFKtZKVK7JOnHWpZNEOORVkR5AtEaoVFM MkTqvcZg5727VjDHeVl1YFCJ+3Eh6f9QwEG1vKfxvygkdN9iwE8a44mkwbGhqGqqe6 geLge/IeNx9EBV3kvleMaIzjDDmfQ6Ts9RLrWzv8e+buz2IIbyzHrwNCd/rzxxjNM7 5YKkrzcyxrkzhjc8p6ZKxGvDO0RWIT87fhA5220Qm2pDZtz7A6L8Kmset3rjQQ6Kvb psVhW82tgtKWptTPfTnTgtI0EQMyWDRmm8oTr6fFHLebyTc6qDhBrJ8OHNqqdbaNmc oWXodFLtCI9+w== Date: Fri, 3 Jul 2026 17:06:33 +0300 From: Mike Rapoport To: Li Zhe Cc: akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, bp@alien8.de, dave.hansen@linux.intel.com, david@kernel.org, kees@kernel.org, mingo@redhat.com, tglx@kernel.org, linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH v5 4/8] mm: add a template-based fast path for zone-device page init Message-ID: References: <20260701090553.62691-1-lizhe.67@bytedance.com> <20260701090553.62691-5-lizhe.67@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260701090553.62691-5-lizhe.67@bytedance.com> X-Stat-Signature: 4p37dwjri9yw7kmzgii7xuuousm4135h X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8475940003 X-HE-Tag: 1783087602-578516 X-HE-Meta: U2FsdGVkX190Y8yr6kHgIlXcEhRZOuiCp55UOjhTi4Ky7qDUuswx5128jKLfLaM220AJFrUnVRa1EOD7v+O1Oc3Ov+O4S6ZhhVdCdIRwMBzzZInm7fk8uQSym8xcp6HYrRjC/+ZEVs6VuwZ9c+FEM2m3PgJY2rDyazZk8oi5qQ79xBY4M2FgAzeZSQMKXdY6zGWZVSX+jlt8tgWItcP2oog/BpkB7oClI7t2oSPBcbxxsHa85nCkwut5DXnhluQ4HFKm9BCjv11axyCGEwjOKPtB898cIcBLThw/NozBQbrQn2wT7DDc82YdD9gXjnu0OY/RVJzW7Y2XdEzvuI+BkTXJqMjFRVliryzaC3+ZYzieDIBNKnjw40LqaUJ89F9Vraeq7PEd4KDm6QDovLMW2UGQJN0PH2fEIN919tJ+Mn8nHle3zGCSSEPxxuW1yhAVRCS9UFJIW/5LLzvbcWj93UsRb8M1L6yxMsQawz/IzKh0TmyMIgOAhZFQBjOeMkDzD6a0KjCEQ36UVdeUHtMOlxQOHvvw8m6B+MKsY8ggHRNJ7a+YaeTuvBC7wobRFWyhZdz8tzFTFZFAMNrMLBJIt3i4X3sd2nIbzGk3MI5lYJ2tb8zKkvWkMYv/luvO9oQKo+IfgMV1j1R5AfckYmE4X5lftttoU/Kl7Ho2J4z+MM9/bKNe1xIV50iVP5jTbNAj0+oJt5CBspEkalonki56LgjWmO35x9YW1fjNoRNMZEtQfCe04nEgk+koZxlA3qGQsx0Zklox+phOX8SlE8oSKwVqW2w76cSMxdqVj+ZhLWarApD1sR4zYAhMjA4Qm3TnDPyD4HlwXWM6sHK7vQO3lJg2h58OuKuwbFDVsB17CJ93Fs/im+QQx6gJGvix6A9DbXdZCr4c6GYArh4D/8GJixzQLuZrdUX+3dwsXSWbKOpnnyEovBy+PjQ3GvHTV3tBaABZQP9Z3c9eU0jnjNW MnPjiRrE hJiuf52oiLB2I9YNnN61/3mla6DvN4ge2jyBXzx0bDeZVpipo4Psbkeo+fPMTS/yjHRgYSu9N+mGrdRjC1YQEQB4WQR53MMl7S8XLYBE1YhZAgNiQqUwTweuJa+rPZcxiBDPfyjcxSUFTSDJqwItdHHsmE5HDELemE8M9geYtBPP3Pkv4hKIdscDjKPg/hQ+8plspczmkVOytPHzZAIna68dtbn8J/BNyl+LFyGrcMsiirVy0wn6kot4QrOlS2SNzPsE+8UdtbsyoZ31M3n6eZJpXUQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 01, 2026 at 05:05:49PM +0800, Li Zhe wrote: > memmap_init_zone_device() repeats nearly identical head-page > initialization for each PFN. Prepare one reusable ZONE_DEVICE head-page > template through the existing slow path, refresh the PFN-dependent > fields in that template before each copy, and memcpy it into each > destination page. > > This reduces the average rebind time from 244.28 ms to 217.19 ms, or > about 11%. > > Signed-off-by: Li Zhe > --- > mm/mm_init.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 74 insertions(+), 2 deletions(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 4c7fad440c2a..cc8417951467 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -1066,6 +1066,50 @@ static void __ref zone_device_page_init_slow(struct page *page, > set_page_count(page, 0); > } > > +static inline bool zone_device_page_init_optimization_enabled(void) > +{ > + /* > + * The template fast path copies a preinitialized struct page image. > + * Skip it when the page_ref_set tracepoint is enabled. > + */ > + return !page_ref_tracepoint_active(page_ref_set); > +} > + > +static inline void zone_device_template_page_init(struct page *template, > + struct page *src) > +{ > + memcpy(template, src, sizeof(*template)); > +} > + > +/* > + * 'template' is a reusable page prototype rather than a strictly immutable > + * object. Most ZONE_DEVICE fields stay constant across the pages covered by > + * the current template, but section bits and page->virtual may still depend > + * on the PFN. Refresh those PFN-dependent fields in the template before > + * copying it into @page. > + */ > +static inline void zone_device_page_update_template(struct page *template, > + unsigned long pfn) > +{ > + set_page_section_from_pfn(template, pfn); > +#ifdef WANT_PAGE_VIRTUAL > + if (!is_highmem_idx(ZONE_DEVICE)) > + set_page_address(template, __va(pfn << PAGE_SHIFT)); > +#endif > +} > + > +static void zone_device_page_init_from_template(struct page *page, > + unsigned long pfn, struct page *template) > +{ > + /* > + * 'template' carries the invariant portion of a ZONE_DEVICE struct > + * page. Update the PFN-dependent fields in place before copying it > + * to the destination page. > + */ > + zone_device_page_update_template(template, pfn); > + memcpy(page, template, sizeof(*page)); > +} > + The whole bunch of template functions look like it could be useful for initialization of the non-zone-device struct pages as well. As I mentioned previously, it's interesting to see if this approach speeds up normal memory map initialization as well. If if does could have a single set of the template functions. -- Sincerely yours, Mike.