On 1/31/23 04:28, Jan Kara wrote: > On Tue 31-01-23 09:32:27, David Hildenbrand wrote: >> On 30.01.23 23:15, Jens Axboe wrote: >>> On 1/30/23 3:12 PM, David Howells wrote: >>>> John Hubbard <jhubbard@xxxxxxxxxx> wrote: >>>> >>>>> This is something that we say when adding pin_user_pages_fast(), >>>>> yes. I doubt that I can quickly find the email thread, but we >>>>> measured it and weren't immediately able to come up with a way >>>>> to make it faster. >>>> >>>> percpu counters maybe - add them up at the point of viewing? >>> >>> They are percpu, see my last email. But for every 108 changes (on >>> my system), they will do two atomic_long_adds(). So not very >>> useful for anything but low frequency modifications. >>> >> >> Can we just treat the whole acquired/released accounting as a debug >> mechanism to detect missing releases and do it only for debug kernels? > > Yes, AFAIK it is just a debug mechanism for helping to find out issues with > page pinning conversions. So I think we can put this behind some debugging > ifdef. John? > Yes, just for debugging. I wrote a little note just now in response to the patch about how we ended up here: "yes, it's time to hide these behind an ifdef". thanks, -- John Hubbard NVIDIA
