Messages in this thread | | | From | "Huang\, Ying" <> | Subject | Re: [PATCH -mm -v3] mm, swap: Sort swap entries before free | Date | Tue, 02 May 2017 13:35:24 +0800 |
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Hi, Minchan,
Minchan Kim <minchan@kernel.org> 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();
Or, we can make nr_swapfiles more correct as Tim suggested (tracking the number of the swap devices during swap on/off).
Best Regards, Huang, Ying
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