On 2026-07-06 at 17:45 +1000, Li Zhe <[email protected]> wrote... > On Fri, 3 Jul 2026 17:06:33 +0300, [email protected] wrote: > > > 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 <[email protected]> > > > --- > > > 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. > > Thanks for the suggestion. I agree this is worth exploring. > > For this series, I would prefer to keep the scope limited to the > ZONE_DEVICE initialization path and get that part settled first.
I think that makes sense, especially as my initial perf testing with other types of ZONE_DEVICE pages without altmap didn't show much of a perf impact. Meaning it might not be so useful for normal page init. > After this series is settled, I plan to look into whether a similar > template-based approach can also help normal page initialization. If it > shows a real benefit there as well, I can follow up with a separate > series. I agree it would be interesting though, please let us know what you find one way or the other. - Alistair > Thanks, > Zhe
