于 2013/7/10 8:31, Joonsoo Kim 写道: > On Thu, Jul 04, 2013 at 12:00:44PM +0200, Michal Hocko wrote: >> On Thu 04-07-13 13:24:50, Joonsoo Kim wrote: >>> On Thu, Jul 04, 2013 at 12:01:43AM +0800, Zhang Yanfei wrote: >>>> On 07/03/2013 11:51 PM, Zhang Yanfei wrote: >>>>> On 07/03/2013 11:28 PM, Michal Hocko wrote: >>>>>> On Wed 03-07-13 17:34:15, Joonsoo Kim wrote: >>>>>> [...] >>>>>>> For one page allocation at once, this patchset makes allocator slower than >>>>>>> before (-5%). >>>>>> >>>>>> Slowing down the most used path is a no-go. Where does this slow down >>>>>> come from? >>>>> >>>>> I guess, it might be: for one page allocation at once, comparing to the original >>>>> code, this patch adds two parameters nr_pages and pages and will do extra checks >>>>> for the parameter nr_pages in the allocation path. >>>>> >>>> >>>> If so, adding a separate path for the multiple allocations seems better. >>> >>> Hello, all. >>> >>> I modify the code for optimizing one page allocation via likely macro. >>> I attach a new one at the end of this mail. >>> >>> In this case, performance degradation for one page allocation at once is -2.5%. >>> I guess, remained overhead comes from two added parameters. >>> Is it unreasonable cost to support this new feature? >> >> Which benchmark you are using for this testing? > > I use my own module which do allocation repeatedly. > >> >>> I think that readahead path is one of the most used path, so this penalty looks >>> endurable. And after supporting this feature, we can find more use cases. >> >> What about page faults? I would oppose that page faults are _much_ more >> frequent than read ahead so you really cannot slow them down. > > You mean page faults for anon? > Yes. I also think that it is much more frequent than read ahead. > Before futher discussion, I will try to add a separate path > for the multiple allocations. Some days ago, I was thinking that this multiple allocation behaviour may be useful for vmalloc allocations. So I think it is worth trying. > > Thanks. > >> >> [...] >> -- >> Michal Hocko >> SUSE Labs >> >> -- >> 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> > -- Thanks. Zhang Yanfei -- 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