Gregory Price <gregory.price@xxxxxxxxxxxx> writes:
> On Tue, Dec 19, 2023 at 11:04:05AM +0800, Huang, Ying wrote:
>> Gregory Price <gourry.memverge@xxxxxxxxx> writes:
>>
>> > This patch set extends the mempolicy interface to enable new
>> > mempolicies which may require extended data to operate.
>> >
>> > MPOL_WEIGHTED_INTERLEAVE is included as an example extension.
>>
>> Per my understanding, it's better to describe why we need this patchset
>> at the beginning. Per my understanding, weighted interleave is used to
>> expand DRAM bandwidth for workloads with real high memory bandwidth
>> requirements. Without it, DRAM bandwidth will be saturated, which leads
>> to poor performance.
>>
>
> Will add more details, thanks.
>
>> > struct mempolicy_args {
>> > unsigned short mode; /* policy mode */
>> > unsigned short mode_flags; /* policy mode flags */
>> > int home_node; /* mbind: use MPOL_MF_HOME_NODE */
>> > nodemask_t *policy_nodes; /* get/set/mbind */
>> > unsigned char *il_weights; /* for mode MPOL_WEIGHTED_INTERLEAVE */
>> > int policy_node; /* get: policy node information */
>> > };
>>
>> Because we use more and more parameters to describe the mempolicy, I
>> think it's a good idea to replace some parameters with struct. But I
>> don't think it's a good idea to put unrelated stuff into the struct.
>> For example,
>>
>> struct mempolicy_param {
>> unsigned short mode; /* policy mode */
>> unsigned short mode_flags; /* policy mode flags */
>> int home_node; /* mbind: use MPOL_MF_HOME_NODE */
>> nodemask_t *policy_nodes;
>> unsigned char *il_weights; /* for mode MPOL_WEIGHTED_INTERLEAVE */
>> };
>>
>> describe the parameters to create the mempolicy. It can be used by
>> set/get_mempolicy() and mbind(). So, I think that it's a good
>> abstraction. But "policy_node" has nothing to do with set_mempolicy()
>> and mbind(). So I think that we shouldn't add it into the struct. It's
>> totally OK to use different parameters for different functions. For
>> example,
>>
>> long do_set_mempolicy(struct mempolicy_param *mparam);
>> long do_mbind(unsigned long start, unsigned long len,
>> struct mempolicy_param *mparam, unsigned long flags);
>> long do_get_task_mempolicy(struct mempolicy_param *mparam, int
>> *policy_node);
>>
>> This isn't the full list. My point is to use separate parameter for
>> something specific for some function.
>>
>
> this is the internal structure, but i get the point, we can drop it from
> the structure and extend the arg list internally.
>
> I'd originally thought to just remove the policy_node stuff all
> together from get_mempolicy2(). Do you prefer to have a separate struct
> for set/get interfaces so that the get interface struct can be extended?
>
> All the MPOL_F_NODE "alternate data fetch" mechanisms from
> get_mempolicy() feel like more of a wart than a feature. And presently
> the only data returned in policy_node is the next allocation node for
> interleave. That's not even particularly useful, so I'm of a mind to
> remove it.
>
> Assuming we remove policy_node altogether... do we still break up the
> set/get interface into separate structures to avoid this in the future?
I have no much experience at ABI definition. So, I want to get guidance
from more experienced people on this.
Is it good to implement all functionality of get_mempolicy() with
get_mempolicy2(), so we can deprecate get_mempolicy() and remove it
finally? So, users don't need to use 2 similar syscalls?
And, IIUC, we will not get policy_node, addr_node, and policy config at
the same time, is it better to use a union instead of struct in
get_mempolicy2()?
>> > struct mpol_args {
>> > /* Basic mempolicy settings */
>> > __u16 mode;
>> > __u16 mode_flags;
>> > __s32 home_node;
>> > __aligned_u64 pol_nodes;
>> > __aligned_u64 *il_weights; /* of size pol_maxnodes */
>> > __u64 pol_maxnodes;
>> > __s32 policy_node;
>> > };
>>
>> Same as my idea above. I think we shouldn't add policy_node for
>> set_mempolicy2()/mbind2(). That will make users confusing. We can use
>> a different struct for get_mempolicy2().
>>
>
> See above.
--
Best Regards,
Huang, Ying
