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SubjectRe: [External] Re: [PATCH v2] mm: add new syscall pidfd_set_mempolicy().
From
Hi Ying, thanks for your replay and suggestions.

>
> I suggest to move the flags in "mode" parameter (MPOL_F_STATIC_NODES,
> MPOL_F_RELATIVE_NODES, MPOL_F_NUMA_BALANCING, etc.) to "flags"
> parameter, otherwise, why add it?

The "flags" is used for future extension if any, just like
process_madvise() and set_mempolicy_home_node().
Maybe it should be removed.

>
> And, how about add a "home_node" parameter? I don't think that it's a
> good idea to add another new syscall for pidfd_set_mempolicy_home_node()
> in the future.
>

Good idea, but "home_node" is used for vma policy, not task policy.
It is possible to use it in pidfd_mbind() in the future.

>
> IMHO, "The first four APIS" and "The last one" isn't easy to be
> understood. How about
>
> "sys_pidfd_set_mempolicy sets the mempolicy of task specified in the
> pidfd, the others affect only the calling task, ...".
>

Got it.

>
> Why add "sys_"? I fount that there's no "sys_" before set_mempolicy()/mbind() etc.
>

Got it.

>> +void mpol_put_async(struct task_struct *task, struct mempolicy *p)
>
> How about change __mpol_put() directly?

>
> Why can we fall back to freeing directly if task_work_add() failed?
> Should we check the return code and fall back only if -ESRCH and WARN
> for other cases?
>

A task_work based solution has not been accepted yet, it will be
considered later if needed.


>> + }
>
> Why do we need to write lock mmap_sem? IIUC, we don't touch vma.
>

Yes, it should be removed.

>> /*
>
> Because we will change task_struct->mempolicy in another task, we need
> to use kind of "load acquire" / "store release" memory order. For
> example, rcu_dereference() / rcu_assign_pointer(), etc.
>
Thanks again for your suggestion.

Best Regards,
Zhongkun

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