Hello, Konstantin. On Fri, Sep 20, 2019 at 10:39:33AM +0300, Konstantin Khlebnikov wrote: > With vm.dirty_write_behind 1 or 2 files are written even faster and Is the faster speed reproducible? I don't quite understand why this would be. > during copying amount of dirty memory always stays around at 16MiB. The following is the test part of a slightly modified version of your test script which should run fine on any modern systems. for mode in 0 1; do if [ $mode == 0 ]; then prefix='' else prefix='systemd-run --user --scope -p MemoryMax=64M' fi echo COPY time $prefix cp -r dummy copy grep Dirty /proc/meminfo echo SYNC time sync rm -fr copy done and the result looks like the following. $ ./test-writebehind.sh SIZE 3.3G dummy COPY real 0m2.859s user 0m0.015s sys 0m2.843s Dirty: 3416780 kB SYNC real 0m34.008s user 0m0.000s sys 0m0.008s COPY Running scope as unit: run-r69dca5326a9a435d80e036435ff9e1da.scope real 0m32.267s user 0m0.032s sys 0m4.186s Dirty: 14304 kB SYNC real 0m1.783s user 0m0.000s sys 0m0.006s This is how we are solving the massive dirtier problem. It's easy, works pretty well and can easily be tailored to the specific requirements. Generic write-behind would definitely have other benefits and also a bunch of regression possibilities. I'm not trying to say that write-behind isn't a good idea but it'd be useful to consider that a good portion of the benefits can already be obtained fairly easily. Thanks. -- tejun
