Hi Huang, On Tue, May 02, 2017 at 01:35:24PM +0800, Huang, Ying wrote: > Hi, Minchan, > > Minchan Kim <minchan@xxxxxxxxxx> writes: > > > On Fri, Apr 28, 2017 at 09:35:37PM +0800, Huang, Ying wrote: > >> In fact, during the test, I found the overhead of sort() is comparable > >> with the performance difference of adding likely()/unlikely() to the > >> "if" in the function. > > > > Huang, > > > > This discussion is started from your optimization code: > > > > if (nr_swapfiles > 1) > > sort(); > > > > I don't have such fast machine so cannot test it. However, you added > > such optimization code in there so I guess it's *worth* to review so > > with spending my time, I pointed out what you are missing and > > suggested a idea to find a compromise. > > Sorry for wasting your time and Thanks a lot for your review and > suggestion! > > When I started talking this with you, I found there is some measurable > overhead of sort(). But later when I done more tests, I found the > measurable overhead is at the same level of likely()/unlikely() compiler > notation. So you help me to find that, Thanks again! > > > Now you are saying sort is so fast so no worth to add more logics > > to avoid the overhead? > > Then, please just drop that if condition part and instead, sort > > it unconditionally. > > Now, because we found the overhead of sort() is low, I suggest to put > minimal effort to avoid it. Like the original implementation, > > if (nr_swapfiles > 1) > sort(); It might confuse someone in future and would make him/her send a patch to fix like we discussed. If the logic is not clear and doesn't have measureable overhead, just leave it which is more simple/clear. > > Or, we can make nr_swapfiles more correct as Tim suggested (tracking > the number of the swap devices during swap on/off). It might be better option but it's still hard to justify the patch because you said it's hard to measure. Such optimiztion patch should be from numbers. -- 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>
