Messages in this thread | | | Date | Sat, 13 Jun 2020 16:41:18 +0100 | From | Al Viro <> | Subject | Re: [RFC 1/3] lib: copy_{from,to}_user using gup & kmap_atomic() |
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On Sat, Jun 13, 2020 at 04:31:02PM +0100, Al Viro wrote: > On Sat, Jun 13, 2020 at 07:12:36PM +0530, afzal mohammed wrote: > > Hi, > > > > On Sat, Jun 13, 2020 at 01:56:15PM +0100, Al Viro wrote: > > > > > Incidentally, what about get_user()/put_user()? _That_ is where it's > > > going to really hurt... > > > > All other uaccess routines are also planned to be added, posting only > > copy_{from,to}_user() was to get early feedback (mentioned in the > > cover letter) > > Sure, but what I mean is that I'd expect the performance loss to be > dominated by that, not by copy_from_user/copy_to_user on large amounts > of data. Especially on the loads like kernel builds - a lot of stat() > and getdents() calls there.
To clarify: stat() means small copy_to_user(), getdents() - a mix of put_user() and small copy_to_user(). I would be very surprised if it does not hurt a lot.
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