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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/1/30 10:29, Chunsheng Luo wrote: > > > 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 >>> --- >>> 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 Sorry, I make a mistake. The mpol_rebind_nodemask() only modifies the nodemask of the vma policy, but doesn't modify the home_node, so the behavior is different from do_mbind(), so you are right. >>> 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 >>> >>> --------------Wi7Mk80Gx0f1i43BERfX4Ynj Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit


On 2024/1/30 10:29, Chunsheng Luo wrote:


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@ustc.edu>
---
 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
Sorry, I make a mistake. The mpol_rebind_nodemask() only modifies the nodemask of the vma policy,
but doesn't modify the home_node, so the behavior is different from do_mbind(), so you are right.
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
--------------Wi7Mk80Gx0f1i43BERfX4Ynj--