Hi Jens, On Wed, Aug 16, 2017 at 09:56:12AM -0600, Jens Axboe wrote: > On 08/15/2017 10:48 PM, Minchan Kim wrote: > > Hi Jens, > > > > On Mon, Aug 14, 2017 at 10:17:09AM -0600, Jens Axboe wrote: > >> On 08/14/2017 09:38 AM, Jens Axboe wrote: > >>> On 08/14/2017 09:31 AM, Minchan Kim wrote: > >>>>> Secondly, generally you don't have slow devices and fast devices > >>>>> intermingled when running workloads. That's the rare case. > >>>> > >>>> Not true. zRam is really popular swap for embedded devices where > >>>> one of low cost product has a really poor slow nand compared to > >>>> lz4/lzo [de]comression. > >>> > >>> I guess that's true for some cases. But as I said earlier, the recycling > >>> really doesn't care about this at all. They can happily coexist, and not > >>> step on each others toes. > >> > >> Dusted it off, result is here against -rc5: > >> > >> http://git.kernel.dk/cgit/linux-block/log/?h=cpu-alloc-cache > >> > >> I'd like to split the amount of units we cache and the amount of units > >> we free, right now they are both CPU_ALLOC_CACHE_SIZE. This means that > >> once we hit that count, we free all of the, and then store the one we > >> were asked to free. That always keeps 1 local, but maybe it'd make more > >> sense to cache just free CPU_ALLOC_CACHE_SIZE/2 (or something like that) > >> so that we retain more than 1 per cpu in case and app preempts when > >> sleeping for IO and the new task on that CPU then issues IO as well. > >> Probably minor. > >> > >> Ran a quick test on nullb0 with 32 sync readers. The test was O_DIRECT > >> on the block device, so I disabled the __blkdev_direct_IO_simple() > >> bypass. With the above branch, we get ~18.0M IOPS, and without we get > >> ~14M IOPS. Both ran with iostats disabled, to avoid any interference > >> from that. > > > > Looks promising. > > If recycling bio works well enough, I think we don't need to introduce > > new split in the path for on-stack bio. > > I will test your version on zram-swap! > > Thanks, let me know how it goes. It's quite possible that we'll need > a few further tweaks, but at least the basis should be there. Sorry for my late reply. I just finished the swap-in testing in with zram-swap which is critical for the latency. For the testing, I made a memcc and put $NR_CPU(mine is 12) processes in there and each processes consumes 1G so total is 12G while my system has 16GB memory so there was no global reclaim. Then, echo 1 > /mnt/memcg/group/force.empty to swap all pages out and then the programs wait my signal to swap in and I trigger the signal to every processes to swap in every pages and measures elapsed time for the swapin. the value is average usec time elapsed swap-in 1G pages for each process and I repeated it 10times and stddev is very stable. swapin: base(with rw_page) 1100806.73(100.00%) no-rw_page 1146856.95(104.18%) Jens's pcp 1146910.00(104.19%) onstack-bio 1114872.18(101.28%) In my test, there is no difference between dynamic bio allocation (i.e., no-rwpage) and pcp approch but onstack-bio is much faster so it's almost same with rw_page. swapout test is to measure elapsed time for "echo 1 > /mnt/memcg/test_group/force.empty' so it's sec unit. swapout: base(with rw_page) 7.72(100.00%) no-rw_page 8.36(108.29%) Jens's pcp 8.31(107.64%) onstack-bio 8.19(106.09%) rw_page's swapout is 6% or more than faster than else. I tried pmbenchmak with no memcg to see the performance in global reclaim. Also, I executed background IO job which reads data from HDD. The value is average usec time elapsed for a page access so smaller is better. base(with rw_page) 14.42(100.00%) no-rw_page 15.66(108.60%) Jens's pcp 15.81(109.64%) onstack-bio 15.42(106.93%) It's similar to swapout test in memcg. 6% or more is not trivial so I doubt we can remove rw_page at this moment. :( I will look into the detail with perf. If you have further optimizations or suggestions, Feel free to say that. I am happy to test it. Thanks. -- 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>
