On Mon, Aug 31, 2026 at 07:16:35PM +0800, Li Zhe wrote: > The template fast path from the previous patch only accelerates head > pages. Compound tails in memmap_init_compound() still go through the > normal initialization path one by one. > > Build separate head and tail templates and reuse one prepared tail > template across the tail pages in a compound range. Head pages preserve > the existing refcount policy, while compound tails always start with a > refcount of 0 after prep_compound_tail(). > > This extends the template-copy fast path to pfns_per_compound > 1. > Tail-page PFN-dependent fields are refreshed in the reusable tail > template before each copy. > > Do not keep a separate non-template fallback for compound tails either. > These pages are still under memmap initialization, and the > initialization-time refcount updates are not part of the observable > lifetime of pages handed out later. > > The impact is controlled for the same reason as for head pages. The > first tail page still seeds the reusable tail template through the > normal tail initialization sequence, and the copied tail pages have the > same final initialized state except for the PFN-dependent fields > refreshed before each copy. > > Tested in a VM with a 100 GB devdax namespace (align=2097152) on Intel > Ice Lake server. This test exercises the dax_pmem rebind path and > measures memmap initialization latency. > > Test procedure: > Unbind and rebind the dax_pmem driver 30 times, collect memmap > initialization time from the pr_debug() output of > memmap_init_zone_device(). > > Base(v7.3-rc1): > Average of rebinds for dax_pmem driver: 191.20 ms > > With this patch and its prerequisites applied: > Average of rebinds for dax_pmem driver: 176.87 ms > > This reduces the average memmap initialization time measured during > rebind from 191.20 ms to 176.87 ms, or about 7.5%. > > Signed-off-by: Li Zhe <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]> > --- > mm/mm_init.c | 24 ++++++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) -- Sincerely yours, Mike.
