[openib-general] kernel VM monitor for memory registration caching

[Matt Leininger]

FWIW here is a link to the quadrics vm patch that David Addison posted
on LKML a couple of months ago.  

http://lkml.org/lkml/2005/4/26/198

  - Matt




On Sun, 2005-07-31 at 13:31 +0300, Gleb Natapov wrote:
> Hello Pete,
> 
> On Fri, Jul 29, 2005 at 01:42:25PM -0400, Pete Wyckoff wrote:
> > I'll be happy to discuss the code with anyone who ends up wanting
> > to use it or improve upon it.
> 
> I glanced over the code and I have couple of questions/improvments.
> 
>  First of all, you have one user_delta per mm that user can poll from 
> userspace. Is it possible to make user_delta to be part of dreg_region
> instead of dreg_context and module will set it whenever
> registration becomes invalid. Field 'invalid' will be added to buf_info
> structure and pointer to it will be passed to kernel at registration
> time.
>  This way the userpace can look up cache and check if registration is
> still valid. No need to rescan cache from userspace, we already scanned
> it once from kernel after all. With your current approach userspace will
> need to search for mr_handle in the cache and invalidate the entry that
> holds it.
> 
> 
>  You change vma_ops in vma to catch open/close events. What about
> nopage() method in vma_ops? We have to forward it to original vma_ops?
> 
> Something like included patch (not even compiled).
> 
> 
> --- dreg.c.org	2005-07-31 13:10:17.375403091 +0300
> +++ dreg.c	2005-07-31 13:24:35.404872561 +0300
> @@ -162,7 +162,10 @@
>  
>      pr_debug("%s: reg %p vma %p addr %lx\n", __func__, reg, vma, reg->addr);
>      if (vma)
> +    {
> +	kfree (vma->vm_ops);
>  	vma->vm_ops = reg->orig_ops;
> +    }
>      if (reg->addr)
>  	mem_deregister(dc, reg);
>      list_del(&reg->subordinate_list);
> @@ -305,6 +308,7 @@
>       * forget about it and do not build a new region for it.
>       */
>      if (list_empty(&temp_new_subordinate_list)) {
> +	kfree (newvma->vm_ops);
>  	newvma->vm_ops = orig_ops;
>      } else {
>  	reg = kmem_cache_alloc(dreg_region_cache, GFP_KERNEL);
> @@ -510,7 +514,7 @@
>        vma->vm_start, vma->vm_end, reg);
>  
>      reg->orig_ops = vma->vm_ops;
> -    if (vma->vm_ops == &dreg_vm_ops) {
> +    if (vma->vm_ops->close == dreg_vm_ops.close) {
>  	/* chain off proper owner */
>  	struct dreg_region *topreg;
>  	pr_debug("%s: marked subordinate\n", __func__);
> @@ -523,10 +527,22 @@
>  	}
>  	list_add(&reg->subordinate_list, &topreg->subordinate_list);
>      } else {
> +	struct vm_operations_struct *tmp_vm_ops;
>  	/* non subordinate */
>  	reg->vma = vma;
>  	INIT_LIST_HEAD(&reg->subordinate_list);
> -	vma->vm_ops = &dreg_vm_ops;  /* own this vma */
> +
> +	tmp_vm_ops = kmalloc (sizeof (struct vm_operations_struct), GFP_KERNEL);
> +	memcpy (tmp_vm_ops, &dreg_vm_ops, sizeof (struct vm_operations_struct));
> +	if (vma->vm_ops)
> +	{
> +		tmp_vm_ops->nopage = vma->vm_ops->nopage;
> +#ifdef CONFIG_NUMA
> +		tmp_vm_ops->set_policy = vma->vm_ops->set_policy;
> +		tmp_vm_ops->get_policy = vma->vm_ops->get_policy;
> +#endif
> +	}
> +	vma->vm_ops = tmp_vm_ops;  /* own this vma */
>  	reg->orig_vm_start = vma->vm_start;
>  	reg->orig_vm_end = vma->vm_end;
>      }
> --
> 			Gleb.
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