On Wed, Nov 06, 2019 at 06:50:25PM -0800, Shakeel Butt wrote: > On Mon, Jun 3, 2019 at 2:59 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > > When applications are put into unconfigured cgroups for memory > > accounting purposes, the cgrouping itself should not change the > > behavior of the page reclaim code. We expect the VM to reclaim the > > coldest pages in the system. But right now the VM can reclaim hot > > pages in one cgroup while there is eligible cold cache in others. > > > > This is because one part of the reclaim algorithm isn't truly cgroup > > hierarchy aware: the inactive/active list balancing. That is the part > > that is supposed to protect hot cache data from one-off streaming IO. > > > > The recursive cgroup reclaim scheme will scan and rotate the physical > > LRU lists of each eligible cgroup at the same rate in a round-robin > > fashion, thereby establishing a relative order among the pages of all > > those cgroups. However, the inactive/active balancing decisions are > > made locally within each cgroup, so when a cgroup is running low on > > cold pages, its hot pages will get reclaimed - even when sibling > > cgroups have plenty of cold cache eligible in the same reclaim run. > > > > For example: > > > > [root@ham ~]# head -n1 /proc/meminfo > > MemTotal: 1016336 kB > > > > [root@ham ~]# ./reclaimtest2.sh > > Establishing 50M active files in cgroup A... > > Hot pages cached: 12800/12800 workingset-a > > Linearly scanning through 18G of file data in cgroup B: > > real 0m4.269s > > user 0m0.051s > > sys 0m4.182s > > Hot pages cached: 134/12800 workingset-a > > > > Can you share reclaimtest2.sh as well? Maybe a selftest to > monitor/test future changes. I wish it were more portable, but it really only does what it says in the log output, in a pretty hacky way, with all parameters hard-coded to my test environment: --- #!/bin/bash # this should protect workingset-a from workingset-b set -e #set -x echo Establishing 50M active files in cgroup A... rmdir /cgroup/workingset-a 2>/dev/null || true mkdir /cgroup/workingset-a echo $$ > /cgroup/workingset-a/cgroup.procs rm -f workingset-a dd of=workingset-a bs=1M count=0 seek=50 2>/dev/null >/dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null cat workingset-a > /dev/null echo -n "Hot pages cached: " ./mincore workingset-a echo -n Linearly scanning through 2G of file data cgroup B: rmdir /cgroup/workingset-b >/dev/null || true mkdir /cgroup/workingset-b echo $$ > /cgroup/workingset-b/cgroup.procs rm -f workingset-b dd of=workingset-b bs=1M count=0 seek=2048 2>/dev/null >/dev/null time ( cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null cat workingset-b > /dev/null ) echo -n "Hot pages cached: " ./mincore workingset-a
