On Tue, Jul 25, 2017 at 05:41:36PM +0200, Peter Zijlstra wrote: > On Wed, May 24, 2017 at 05:59:41PM +0900, Byungchul Park wrote: > > We can skip adding a dependency 'AX -> B', in case that we ensure 'AX -> > > the previous of B in hlocks' to be created, where AX is a crosslock and > > B is a typical lock. Remember that two adjacent locks in hlocks generate > > a dependency like 'prev -> next', that is, 'the previous of B in hlocks > > -> B' in this case. > > > > For example: > > > > in hlocks[] > > ------------ > > ^ A (gen_id: 4) --+ > > | | previous gen_id > > | B (gen_id: 3) <-+ > > | C (gen_id: 3) > > | D (gen_id: 2) > > oldest | E (gen_id: 1) > > > > in xhlocks[] > > ------------ > > ^ A (gen_id: 4, prev_gen_id: 3(B's gen id)) > > | B (gen_id: 3, prev_gen_id: 3(C's gen id)) > > | C (gen_id: 3, prev_gen_id: 2(D's gen id)) > > | D (gen_id: 2, prev_gen_id: 1(E's gen id)) > > oldest | E (gen_id: 1, prev_gen_id: NA) > > > > On commit for a crosslock AX(gen_id = 3), it's engough to add 'AX -> C', > > but adding 'AX -> B' and 'AX -> A' is unnecessary since 'AX -> C', 'C -> > > B' and 'B -> A' cover them, which are guaranteed to be generated. > > > > This patch intoduces a variable, prev_gen_id, to avoid adding this kind > > of redundant dependencies. In other words, the previous in hlocks will > > anyway handle it if the previous's gen_id >= the crosslock's gen_id. > > > > Didn't we talk about an alternative to this? Yes, we did. You said the optimazation was unnecessary, and I was not sure if it's true, so added it at this time. But *I will exclude this from next spin*. > > /me goes dig > > https://lkml.kernel.org/r/20170303091338.GH6536@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > There and replies. > > So how much does this save vs avoiding redundant links? No different on my qemu machine. The answer was: https://lkml.org/lkml/2017/3/14/103 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
