Hi, Michal On 2025/11/14 01:07, Michal Koutný wrote: >On Thu, Nov 13, 2025 at 09:14:34PM +0800, Sun Shaojie <[email protected]> >wrote: >> In cgroup v2, a mutual overlap check is required when at least one of two >> cpusets is exclusive. However, this check should be relaxed and limited to >> cases where both cpusets are exclusive. >> >> The table 1 shows the partition states of A1 and B1 after each step before >> applying this patch. >> >> Table 1: Before applying the patch >> Step | A1's prstate | B1's prstate | >> #1> mkdir -p A1 | member | | >> #2> echo "0-1" > A1/cpuset.cpus | member | | >> #3> echo "root" > A1/cpuset.cpus.partition | root | | >> #4> mkdir -p B1 | root | member | >> #5> echo "0-3" > B1/cpuset.cpus | root invalid | member | >> #6> echo "root" > B1/cpuset.cpus.partition | root invalid | root invalid | >> >> After step #5, A1 changes from "root" to "root invalid" because its CPUs >> (0-1) overlap with those requested by B1 (0-3). However, B1 can actually >> use CPUs 2-3, so it would be more reasonable for A1 to remain as "root." > >I remember there was the addition of cgroup_file_notify() for the >cpuset.cpus.partition so that such changes can be watched for. > >I may not be seeing whole picture, so I ask -- why would it be "more >reasonable" for A1 to remain root. From this description it looks like >you'd silently convert B1's effective cpus to 2-3 but IIUC the code >change that won't happen but you'd reject the write of "0-3" instead. >
The desired outcome is that after step #5, although B1 writes "0-3" to cpuset.cpus, A1 can still remain as "root", and B1 ends up with effective CPUs of 2-3. In summary, We want to avoid A1's invalidation when B1 changes its cpuset.cpus. Because cgroup v2 allows the effective CPU mask of a cpuset to differ from its requested mask. Indeed, this issue was discussed in detail during the v1 review. https://lore.kernel.org/cgroups/[email protected]/T/#u >Isn't here missing Table 2: After applying the patch? I'm asking because >of the number 1 but also because it'd make the intention clearer >;-), perhaps with a column for cpuset.cpus.effective. Thanks for the suggestion. I will update the patch description accordingly. Thanks, Sun Shaojie
