On Mon, Jun 8, 2020 at 1:09 PM afzal mohammed <afzal.mohd...@gmail.com> wrote: > On Sun, Jun 07, 2020 at 05:11:16PM +0100, Russell King - ARM Linux admin > wrote: > > On Sun, Jun 07, 2020 at 06:29:32PM +0530, afzal mohammed wrote: > > > > get_user_pages_fast() followed by kmap_atomic() & then memcpy() seems > > > to work in principle for user copy. > > > > Have you done any performance evaluation of the changes yet? I think > > it would be a good idea to keep that in the picture. If there's any > > significant regression, then that will need addressing. > > Not yet. Yes, i will do the performance evaluation. > > i am also worried about the impact on performance as these > [ get_user_pages() or friends, kmap_atomic() ] are additionally > invoked in the copy_{from,to}_user() path now.
I am happy to help! I am anyway working on MMU-related code (KASan) so I need to be on top of this stuff. What test is appropriate for this? I would intuitively think hackbench? > Note that this was done on a topic branch for user copy. Changes for > kernel static mapping to vmalloc has not been merged with these. > Also having kernel lowmem w/ a separate asid & switching at kernel > entry/exit b/n user & kernel lowmem by changing ttbr0 is yet to be > done. Quite a few things remaining to be done to achieve vmsplit 4g/4g I will be very excited to look at patches or a git branch once you have something you want to show. Also to just understand how you go about this. I have several elder systems under my roof so my contribution could hopefully be to help and debug any issues on these. Yours, Linus Walleij