On 6/10/19 4:20 PM, H.J. Lu wrote: >>> Perhaps we still let the app fill the bitmap? >> I think I'd want to see some performance data on it first. > Updating legacy bitmap in user space from kernel requires > > long q; > > get_user(q, ...); > q |= mask; > put_user(q, ...); > > instead of > > *p |= mask; > > get_user + put_user was quite slow when we tried before.
Numbers, please. There are *lots* of ways to speed something like that up if you have actual issues with it. For instance, you can skip the get_user() for whole bytes. You can write bits with 0's for unallocated address space. You can do user_access_begin/end() to avoid bunches of STAC/CLACs... The list goes on and on. :)
