On Fri, 2 Mar 2018 16:01:25 +0800 Aaron Lu <aaron.lu@xxxxxxxxx> wrote: > On Thu, Mar 01, 2018 at 04:01:05PM -0800, Andrew Morton wrote: > > On Thu, 1 Mar 2018 14:28:44 +0800 Aaron Lu <aaron.lu@xxxxxxxxx> wrote: > > > > > When freeing a batch of pages from Per-CPU-Pages(PCP) back to buddy, > > > the zone->lock is held and then pages are chosen from PCP's migratetype > > > list. While there is actually no need to do this 'choose part' under > > > lock since it's PCP pages, the only CPU that can touch them is us and > > > irq is also disabled. > > > > > > Moving this part outside could reduce lock held time and improve > > > performance. Test with will-it-scale/page_fault1 full load: > > > > > > kernel Broadwell(2S) Skylake(2S) Broadwell(4S) Skylake(4S) > > > v4.16-rc2+ 9034215 7971818 13667135 15677465 > > > this patch 9536374 +5.6% 8314710 +4.3% 14070408 +3.0% 16675866 +6.4% > > > > > > What the test does is: starts $nr_cpu processes and each will repeatedly > > > do the following for 5 minutes: > > > 1 mmap 128M anonymouse space; > > > 2 write access to that space; > > > 3 munmap. > > > The score is the aggregated iteration. > > > > But it's a loss for uniprocessor systems: it adds more code and adds an > > additional pass across a list. > > Performance wise, I assume the loss is pretty small and can not > be measured. > > On my Sandybridge desktop, with will-it-scale/page_fault1/single process > run to emulate uniprocessor system, the score is(average of 3 runs): > > base(patch 1/3): 649710 > this patch: 653554 +0.6% Does that mean we got faster or slower? > prefetch(patch 3/3): 650336 (in noise range compared to base) > > On 4 sockets Intel Broadwell with will-it-scale/page_fault1/single > process run: > > base(patch 1/3): 498649 > this patch: 504171 +1.1% > prefetch(patch 3/3): 506334 +1.5% (compared to base) > > It looks like we don't need to worry too much about performance for > uniprocessor system. Well. We can say that of hundreds of patches. And we end up with a fatter and slower kernel than we otherwise would. Please take a look, see if there's a tidy way of avoiding this. Probably there isn't, in which case oh well. But let's at least try. -- 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>
