On Tue, Oct 16, 2012 at 08:50:49AM +0800, Shaohua Li wrote: > On Mon, Oct 08, 2012 at 03:09:58PM -0700, Hugh Dickins wrote: > > On Thu, 4 Oct 2012, Konstantin Khlebnikov wrote: > > > > > Here results of my test. Workload isn't very realistic, but at least it > > > threaded: compiling linux-3.6 with defconfig in 16 threads on tmpfs, > > > 512mb ram, dualcore cpu, ordinary hard disk. (test script in attachment) > > > > > > average results for ten runs: > > > > > > RA=3 RA=0 RA=1 RA=2 RA=4 Hugh Shaohua > > > real time 500 542 528 519 500 523 522 > > > user time 738 737 735 737 739 737 739 > > > sys time 93 93 91 92 96 92 93 > > > pgmajfault 62918 110533 92454 78221 54342 86601 77229 > > > pgpgin 2070372 795228 1034046 1471010 3177192 1154532 1599388 > > > pgpgout 2597278 2022037 2110020 2350380 2802670 2286671 2526570 > > > pswpin 462747 138873 202148 310969 739431 232710 341320 > > > pswpout 646363 502599 524613 584731 697797 568784 628677 > > > > > > So, last two columns shows mostly equal results: +4.6% and +4.4% in > > > comparison to vanilla kernel with RA=3, but your version shows more stable > > > results (std-error 2.7% against 4.8%) (all this numbers in huge table in > > > attachment) > > > > Thanks for doing this, Konstantin, but I'm stuck for anything much to say! > > Shaohua and I are both about 4.5% bad for this particular test, but I'm > > more consistently bad - hurrah! > > > > I suspect (not a convincing argument) that if the test were just slightly > > different (a little more or a little less memory, SSD instead of hard > > disk, diskcache instead of tmpfs), then it would come out differently. > > > > Did you draw any conclusions from the numbers you found? > > > > I haven't done any more on this in the last few days, except to verify > > that once an anon_vma is judged random with Shaohua's, then it appears > > to be condemned to no-readahead ever after. > > > > That's probably something that a hack like I had in mine would fix, > > but that addition might change its balance further (and increase vma > > or anon_vma size) - not tried yet. > > > > All I want to do right now, is suggest to Andrew that he hold Shaohua's > > patch back from 3.7 for the moment: I'll send a response to Sep 7th's > > mm-commits mail to suggest that - but no great disaster if he ignores me. > > Ok, I tested Hugh's patch. My test is a multithread random write workload. > With Hugh's patch, 49:28.06elapsed > With mine, 43:23.39elapsed > There is 12% more time used with Hugh's patch. > > In the stable state of this workload, SI:SO ratio should be roughly 1:1. With > Hugh's patch, it's around 1.6:1, there is still unnecessary swapin. > > I also tried a workload with seqential/random write mixed, Hugh's patch is 10% > bad too. With below change, the si/so ratio is back to around 1:1 in my workload. Guess the run time of my test will be reduced too, though I didn't test yet. - used = atomic_xchg(&swapra_hits, 0) + 1; + used = atomic_xchg(&swapra_hits, 0); I'm wondering how could a global counter based method detect readahead correctly. For example, if there are a sequential access thread and a random access thread, doesn't this method always make wrong decision? Thanks, Shaohua -- 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>