linux-kernel - Re: [PATCH v3 4/4] mm/mempolicy: change cur_il_weight to atomic and carry the node with it

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Date: Tue, 30 Jan 2024 11:15:35 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Gregory Price <gregory.price@...verge.com>
Cc: Gregory Price <gourry.memverge@...il.com>,  <linux-mm@...ck.org>,
  <linux-kernel@...r.kernel.org>,  <linux-doc@...r.kernel.org>,
  <linux-fsdevel@...r.kernel.org>,  <linux-api@...r.kernel.org>,
  <corbet@....net>,  <akpm@...ux-foundation.org>,  <honggyu.kim@...com>,
  <rakie.kim@...com>,  <hyeongtak.ji@...com>,  <mhocko@...nel.org>,
  <vtavarespetr@...ron.com>,  <jgroves@...ron.com>,
  <ravis.opensrc@...ron.com>,  <sthanneeru@...ron.com>,
  <emirakhur@...ron.com>,  <Hasan.Maruf@....com>,
  <seungjun.ha@...sung.com>,  <hannes@...xchg.org>,
  <dan.j.williams@...el.com>
Subject: Re: [PATCH v3 4/4] mm/mempolicy: change cur_il_weight to atomic and
 carry the node with it

Gregory Price <gregory.price@...verge.com> writes:

> On Mon, Jan 29, 2024 at 10:48:47AM -0500, Gregory Price wrote:
>> On Mon, Jan 29, 2024 at 04:17:46PM +0800, Huang, Ying wrote:
>> > Gregory Price <gregory.price@...verge.com> writes:
>> > 
>> > But, in contrast, it's bad to put task-local "current weight" in
>> > mempolicy.  So, I think that it's better to move cur_il_weight to
>> > task_struct.  And maybe combine it with current->il_prev.
>> > 
>> Style question: is it preferable add an anonymous union into task_struct:
>> 
>> union {
>>     short il_prev;
>>     atomic_t wil_node_weight;
>> };
>> 
>> Or should I break out that union explicitly in mempolicy.h?
>> 
>
> Having attempted this, it looks like including mempolicy.h into sched.h
> is a non-starter.  There are build issues likely associated from the
> nested include of uapi/linux/mempolicy.h
>
> So I went ahead and did the following.  Style-wise If it's better to just
> integrate this as an anonymous union in task_struct, let me know, but it
> seemed better to add some documentation here.
>
> I also added static get/set functions to mempolicy.c to touch these
> values accordingly.
>
> As suggested, I changed things to allow 0-weight in il_prev.node_weight
> adjusted the logic accordingly. Will be testing this for a day or so
> before sending out new patches.
>

Thanks about this again.  It seems that we don't need to touch
task->il_prev and task->il_weight during rebinding for weighted
interleave too.

For weighted interleaving, il_prev is the node used for previous
allocation, il_weight is the weight after previous allocation.  So
weighted_interleave_nodes() could be as follows,

unsigned int weighted_interleave_nodes(struct mempolicy *policy)
{
        unsigned int nid;
        struct task_struct *me = current;

        nid = me->il_prev;
        if (!me->il_weight || !node_isset(nid, policy->nodes)) {
                nid = next_node_in(...);
                me->il_prev = nid;
                me->il_weight = weights[nid];
        }
        me->il_weight--;

        return nid;
}

If this works, we can just add il_weight into task_struct.

--
Best Regards,
Huang, Ying