From: Matthew Wilcox > Sent: 19 August 2020 16:45 > > On Wed, Aug 19, 2020 at 03:41:48PM +0000, David Laight wrote: > > Does linux have an O(1) (or do I mean o(1)) pid allocator? > > Or does it have to do a linear scan to find a gap?? > > O(log(n)). It uses the IDR allocator, so 'n' in this case is the > number of PIDs currently allocated, and it's log_64 rather than log_2 > (which makes no difference to O() but does make a bit of a difference > to performance) Still worse that O(1) - when that is just replacing a variable with a value read out of an array. Made pid lookup a trivial O(1) as well. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
