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?
> > 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.
~Gregory
