Messages in this thread | | | Date | Tue, 26 Apr 2022 22:34:21 -0400 | Subject | Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init_smp() | From | Waiman Long <> |
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On 4/26/22 21:06, Feng Tang wrote: > On Tue, Apr 26, 2022 at 10:58:21PM +0800, Waiman Long wrote: >> On 4/25/22 23:23, Feng Tang wrote: >>> Hi Waiman, >>> >>> On Mon, Apr 25, 2022 at 11:55:05AM -0400, Waiman Long wrote: >>>> There are 3 places where the cpu and node masks of the top cpuset can >>>> be initialized in the order they are executed: >>>> 1) start_kernel -> cpuset_init() >>>> 2) start_kernel -> cgroup_init() -> cpuset_bind() >>>> 3) kernel_init_freeable() -> do_basic_setup() -> cpuset_init_smp() >>>> >>>> The first cpuset_init() function just sets all the bits in the masks. >>>> The last one executed is cpuset_init_smp() which sets up cpu and node >>>> masks suitable for v1, but not v2. cpuset_bind() does the right setup >>>> for both v1 and v2. >>>> >>>> For systems with cgroup v2 setup, cpuset_bind() is called once. For >>>> systems with cgroup v1 setup, cpuset_bind() is called twice. It is >>>> first called before cpuset_init_smp() in cgroup v2 mode. Then it is >>>> called again when cgroup v1 filesystem is mounted in v1 mode after >>>> cpuset_init_smp(). >>>> >>>> [ 2.609781] cpuset_bind() called - v2 = 1 >>>> [ 3.079473] cpuset_init_smp() called >>>> [ 7.103710] cpuset_bind() called - v2 = 0 >>> I run some test, on a server with centOS, this did happen that >>> cpuset_bind() is called twice, first as v2 during kernel boot, >>> and then as v1 post-boot. >>> >>> However on a QEMU running with a basic debian rootfs image, >>> the second call of cpuset_bind() didn't happen. >> The first time cpuset_bind() is called in cgroup_init(), the kernel >> doesn't know if userspace is going to mount v1 or v2 cgroup. By default, >> it is assumed to be v2. However, if userspace mounts the cgroup v1 >> filesystem for cpuset, cpuset_bind() will be run at this point by >> rebind_subsystem() to set up cgroup v1 environment and >> cpus_allowed/mems_allowed will be correctly set at this point. Mounting >> the cgroup v2 filesystem, however, does not cause rebind_subsystem() to >> run and hence cpuset_bind() is not called again. >> >> Is the QEMU setup not mounting any cgroup filesystem at all? If so, does >> it matter whether v1 or v2 setup is used? > When I got the cpuset binding error report, I tried first on qemu to > reproduce and failed (due to there was no memory hotplug), then I > reproduced it on a real server. For both system, I used "cgroup_no_v1=all" > cmdline parameter to test cgroup-v2, could this be the reason? (TBH, > this is the first time I use cgroup-v2). > > Here is the info dump: > > # mount | grep cgroup > tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755) > cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd) > > #cat /proc/filesystems | grep cgroup > nodev cgroup > nodev cgroup2 > > Thanks, > Feng
For cgroup v2, cpus_allowed should be set to cpu_possible_mask and mems_allowed to node_possible_map as is done in the first invocation of cpuset_bind(). That is the correct behavior.
Cheers, Longman
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