On Mon, Aug 31, 2026 at 07:16:34PM +0800, Li Zhe wrote: > memmap_init_zone_device() repeats nearly identical head-page > initialization for each PFN. Initialize the first real ZONE_DEVICE head > page through the existing path, copy that final state into a reusable > template, refresh the PFN-dependent fields in that template before each > copy, and copy it into the remaining destination pages. > > Use the template path unconditionally. The page_ref_set tracepoint is > primarily a debugging aid, while this code is still initializing struct > pages before they are handed out. From the perspective of users of those > pages, the initialization-time refcount transitions are not part of the > observable page lifetime. > > This means page_ref_set will no longer observe every initialization-time > refcount assignment for copied ZONE_DEVICE head pages. The impact is > controlled because the final initialized struct page state is unchanged, > and keeping a separate non-template path only for this local tracepoint > observability would add complexity to the common path. > > This patch accelerates head-page initialization. The pfns_per_compound > == 1 case gets the full benefit here, compound tails are handled in the > next patch. > > Tested in a VM with a 100 GB fsdax namespace device configured with > map=dev on Intel Ice Lake server. This test exercises the nd_pmem rebind > path (pfns_per_compound == 1). > > Test procedure: > Rebind the nd_pmem driver 30 times and collect the memmap initialization > time from the pr_debug() output of memmap_init_zone_device(). > > Base(v7.3-rc1): > Average of rebinds for nd_pmem driver: 221.07 ms > > With this patch and its prerequisites applied: > Average of rebinds for nd_pmem driver: 155.00 ms > > This reduces the average memmap initialization time measured during > rebind from 221.07 ms to 155.00 ms, or about 29.9%. > > Signed-off-by: Li Zhe <[email protected]>
With one nit below Reviewed-by: Mike Rapoport (Microsoft) <[email protected]> > --- > mm/mm_init.c | 38 +++++++++++++++++++++++++++++++++++--- > 1 file changed, 35 insertions(+), 3 deletions(-) > > @@ -1093,10 +1106,29 @@ void __ref memmap_init_zone_device(struct zone *zone, > nr_pages = end_pfn - start_pfn; > } > > - for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) { > - struct page *page = pfn_to_page(pfn); > + if (!nr_pages) > + return; > > - __init_zone_device_page(page, pfn, zone_idx, nid, pgmap); > + /* > + * Seed the reusable head-page template from the first real struct > + * page. The normal page-init and refcount helpers must operate on > + * a real memmap entry rather than a stack object. > + */ > + pfn = start_pfn; > + page = pfn_to_page(pfn); > + __init_zone_device_page(page, pfn, zone_idx, nid, pgmap); > + memcpy(&template, page, sizeof(*page)); > + if (pfns_per_compound != 1) > + memmap_init_compound(page, pfn, zone_idx, nid, pgmap, > + compound_nr_pages(pfn, altmap, pgmap)); > + pfn += pfns_per_compound; > + > + /* Initialize the remaining head pages from template. */ > + for (; pfn < end_pfn; pfn += pfns_per_compound) { > + page = pfn_to_page(pfn); > + > + zone_device_page_init_from_template(page, pfn, > + &template); Nit: this seems to fit into 80-chars line without wrapping. > > if (IS_ALIGNED(pfn, PAGES_PER_SECTION)) > cond_resched(); > -- > 2.20.1 -- Sincerely yours, Mike.
