Re: [PATCH 19/33] autonuma: memory follows CPU algorithm and task/mm_autonuma stats collection

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

> +
> +bool numa_hinting_fault(struct page *page, int numpages)
> +{
> +	bool migrated = false;
> +
> +	/*
> +	 * "current->mm" could be different from the "mm" where the
> +	 * NUMA hinting page fault happened, if get_user_pages()
> +	 * triggered the fault on some other process "mm". That is ok,
> +	 * all we care about is to count the "page_nid" access on the
> +	 * current->task_autonuma, even if the page belongs to a
> +	 * different "mm".
> +	 */
> +	WARN_ON_ONCE(!current->mm);

Given the above comment, Do we really need this warn_on?
I think I have seen this warning when using autonuma.

> +	if (likely(current->mm && !current->mempolicy && autonuma_enabled())) {
> +		struct task_struct *p = current;
> +		int this_nid, page_nid, access_nid;
> +		bool new_pass;
> +
> +		/*
> +		 * new_pass is only true the first time the thread
> +		 * faults on this pass of knuma_scand.
> +		 */
> +		new_pass = p->task_autonuma->task_numa_fault_pass !=
> +			p->mm->mm_autonuma->mm_numa_fault_pass;
> +		page_nid = page_to_nid(page);
> +		this_nid = numa_node_id();
> +		VM_BUG_ON(this_nid < 0);
> +		VM_BUG_ON(this_nid >= MAX_NUMNODES);
> +		access_nid = numa_hinting_fault_memory_follow_cpu(page,
> +								  this_nid,
> +								  page_nid,
> +								  new_pass,
> +								  &migrated);
> +		/* "page" has been already freed if "migrated" is true */
> +		numa_hinting_fault_cpu_follow_memory(p, access_nid,
> +						     numpages, new_pass);
> +		if (unlikely(new_pass))
> +			/*
> +			 * Set the task's fault_pass equal to the new
> +			 * mm's fault_pass, so new_pass will be false
> +			 * on the next fault by this thread in this
> +			 * same pass.
> +			 */
> +			p->task_autonuma->task_numa_fault_pass =
> +				p->mm->mm_autonuma->mm_numa_fault_pass;
> +	}
> +
> +	return migrated;
> +}
> +

-- 
Thanks and Regards
Srikar

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