On 2024/1/29 23:12, Gregory Price
wrote:
On Fri, Jan 26, 2024 at 08:22:40AM -0500, Chunsheng Luo wrote:set_mempolicy_home_node should be used after setting the memory policy. If the home_node isn't in the nodes of policy, we should return failure to avoid misunderstanding. Signed-off-by: Chunsheng Luo <luochunsheng@xxxxxxxx> --- mm/mempolicy.c | 6 ++++++ 1 file changed, 6 insertions(+)Since it's not possible to add/remove a node to a mask without also erasing the home node, this seems reasonable. e.g. this is what happens presently mbind(0-2) : mask(0,1,2), home_node(NUMA_NO_NODE) home_node(3) : mask(0,1,2), home_node(3) mbind(0-3) : mask(0,1,2,3), home_node(NUMA_NO_NODE) However, it is possible for a cgroup migration or a change to cpusets.mems_allowed to change a nodemask without somping the home_node. e.g.: mbind(2-3) : mask(2-3), home_node(NUMA_NO_NODE) home_node(3) : mask(2-3), home_node(3) cpusets(0-1) : mask(0-1), home_node(3) Should the rebind code also shift the home-node or un-set it accordingly to keep the mask/home_node behavior consistent with the syscalls? (see mpol_rebind_nodemask)
Thank you for your reply.
First, home_node can only be set for VMA policy.
second, the result of cgroup migration is consistent with the result of the first e.g.
when process mem_allowed updates, vma policy will alse be updated.
Function call:
update_tasks_nodemask
->mpol_rebind_mm
-> for_each_vma: mpol_rebind_policy
-> mpol_rebind_nodemask
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 10a590ee1c89..9282be2ae18e 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1536,6 +1536,12 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le err = -EOPNOTSUPP; break; } + + if (!node_isset(home_node, old->nodes)) { + err = -EINVAL; + break; + } + new = mpol_dup(old); if (IS_ERR(new)) { err = PTR_ERR(new); -- 2.43.0
