On Tue, 2 Jul 2024 02:09:31 +0000 Wei Yang <richard.weiyang@xxxxxxxxx> wrote: > The prefetchw() is introduced from an ancient patch[1]. > > The change log says: > > The basic idea is to free higher order pages instead of going > through every single one. Also, some unnecessary atomic operations > are done away with and replaced with non-atomic equivalents, and > prefetching is done where it helps the most. For a more in-depth > discusion of this patch, please see the linux-ia64 archives (topic > is "free bootmem feedback patch"). > > So there are several changes improve the bootmem freeing, in which the > most basic idea is freeing higher order pages. And as Matthew says, > "Itanium CPUs of this era had no prefetchers." > > I did 10 round bootup tests before and after this change, the data > doesn't prove prefetchw() help speeding up bootmem freeing. The sum of > the 10 round bootmem freeing time after prefetchw() removal even 5.2% > faster than before. I don't think I've ever seen prefetch make a damn bit of difference. > [1]: https://lore.kernel.org/linux-ia64/40F46962.4090604@xxxxxxx/ > > Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> > CC: David Hildenbrand <david@xxxxxxxxxx> > > --- > The patch is based on mm-stable with David's change. Oh help. David makes many changes. Please identify patches with much care. Fully quoting the email title works, as does a link.
